Magnetic disk having an improved surface configuration

ABSTRACT

A magnetic disk includes a non-magnetic substrate with a surface processed layer having fine irregularities formed at least on a main surface thereof, and at least thin film magnetic film and a protective film formed in that order on the non-magnetic substrate in such a manner that the fine irregularities are duplicated thereof. The surface of the surface processed layer of the non-magnetic substrate has protrusions whose surfaces are made flat and a configuration which exhibits a three-dimensional bearing curve in which the bearing ratio at a section taken at a depth from the top of the surface which corresponds to the portion of the top portion deformed by the head load during the contact start-stops drive is between 0.1% and 10%. The protrusions formed on the surface processed layer have a height ranging from several nm to several tens of nm. The bearing ratio is a value obtained at a depth of 5 to 10 nm from the top of the protrusions.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a magnetic disk, a method of and anapparatus for manufacturing the same, and a magnetic disk unit obtainedby the same. More particularly, the present invention pertains to amagnetic disk of the type which employs a thin magnetic film as arecording medium, which enables the floating characteristics of amagnetic head thereto to be improved, and which exhibits improvedsliding-resistant characteristics thereof, a method of and an apparatusfor manufacturing the same, and a magnetic disk unit obtained by thesame.

In high-density and large-capacity magnetic disks, the magneticrecording medium formed on a non-magnetic disk substrate isconventionally a coated film formed by coating magnetic powders heldtogether by a resin on the recording medium. However, use of this coatedfilm has been giving way in recent years to use of a thin magnetic metallayer directly formed on the disk substrate by deposition or sputtering.When the magnetic disk units is driven, the magnetic disk (hereinafterreferred to merely as "the disk") is housed in a magnetic disk units ina stationary state with a magnetic head (hereinafter referred to merelyas "a head") having a specific load being elastically in contact andpressed against the surface of the disk. Then, the magnetic disk isnormally driven by the contact start stop (abbreviated to CSS) method asfollows: as the disk starts rotating, the head starts sliding againstthe surface of the disk. Once the rotational speed of the disk reaches avalue as high as 1000 rpm i.e. high speed rotation, the head floats inthe air at a predetermined distance from the surface of the disk due tothe dynamic pressure effects caused by the air flow generated betweenthe sliding surface of the head and the disk. The magnetic head unit isarranged such that the head can be freely moved in the radial directionof the disk in this floating state so as to allow data to be stored onand retrieved from the surface of the disk at a desired position. Whenthe operation of the disk drive is to be stopped, the rotational speedof the disk decreases, and thus the head starts sliding against thesurface of the disk again. The head then stops in a state in which it isin contact with and presses against the disk. In this CSS drivingmethod, each time the head and disk assembly is driven, the slidingsurface of the head repeats a cyclic operation, consisting of stopping,sliding against the surface of the disk, floating in the air, slidingagainst the surface of the disk, and stopping. In order to facilitatefloating of the head, the surface of the disk is generally provided withmicro grooves which extend in the circumferential direction thereof.FIG. 10 shows a section of a disk 80. When the grooves of this type areto be formed, the surface of a disk substrate 30 is subjected to thesurface polishing process called texture process prior to the formationof the magnetic film. Thereafter, a thin magnetic layer 32, a protectivefilm 33 and a lubricating film (not shown) are formed on the irregularsurface of the substrate, by means of which the grooves formed in thesurface of the disk substrate are reproduced on the surface of the disk.

The texture process to which the disk surface is subjected is apolishing technique essential to the magnetic disk which is driven bythe CSS driving method. For example, Japanese Patent UnexaminedPublication No. 62-219227 discloses that, when the disk surface ispolished to a maximum surface roughness of 0.02 to 0.1 μm, the thicknessof a non-magnetic metal film (Cr film) can be reduced and productivitycan thus be improved. It has also been disclosed that, when the CSS testwas conducted 20,000 times on such a magnetic disk, no damage occurredon the surface of the disk while head crashing easily occurred on thesurface of the disk having a surface roughness of 0.1 μm or above, andthat, when the disk surface was not subjected to the texture process, itwas damaged and head crashing occurred when CSS was conducted 5000times.

FIG. 12 shows a conventional texture processing device which isdisclosed in Japanese Patent Unexamined Publication No. 54-23294. Inthis device, the two surfaces of the disk substrate 30 aresimultaneously processed by pressing polishing tapes 4, which are movedin a vertical direction by the rotation of reels 6, in the directionindicated by the arrow toward the two surfaces of the rotating disksubstrate 30 by means of contact rollers 8 while moving back and forthin the radial direction of the disk substrate. FIGS. 7 and 8 are frontand side elevational views showing the positional relation between thesubstrate 30 and the polishing tapes 4 which are moving along thesubstrate 30. In this texture process, a micro groove 37 such as thatshown in FIG. 11, can be formed by the polishing tape. However,formation of the groove causes an unstable rising portion 36 to beformed at the shoulder of the groove. The rising portion 36 remains onthe surface of the disk as a fine protrusion.

Hence, it has been proposed to conduct on the surface of the disksubstrate a first polishing process which is a normal polishing processand then a second polishing process which employes abrasive grainssmaller than those employed in the first polishing process to removeonly the protrusions generated on the surface of the substrate by thefirst polishing process without removing the micro grooves formed in thesurface of the substrate. Such a technique is disclosed in JapanesePatent Unexamined Publication No. 62-248133.

The maximum surface roughness of the disk substrate on which microgrooves are formed by the texture process and protrusions formed on thesubstrate in order to achieve improvement in the head floating have beenspecified. However, the optimal conditions of the surface which issubjected to the texture process in terms of the CSS characteristics andhead adhesion characteristics are unknown, and the problems involvinghead crashing or the like have not yet been solved.

As high-density and large-capacity magnetic disks have been developed inrecent years, the distance which the head floats above the surface ofthe disk in the CSS drive is becoming shorter and shorter. For example,it is required under severe condition that the gap between the surfaceof the disk and the sliding surface of the head (which is the distanceby which the head floats above the surface of the disk), which isfloating above the disk surface due to the rotation of the disk, be 0.2μm or less. Hence, in order to realize this severe condition by means ofthe texture process, the height of the protrusions rising at theshoulders of the grooves must be suppressed at less than the distance bywhich the head floats up, so that it must be avoided for the head tocollide against the protrusions. Thus, very strict surfacecharacteristics of the disk is required. If only contact of theprotrusions against the head sliding surface must be avoided, the headcan be provided with a sufficient floating distance by changing theconfiguration of the head sliding surface, the leads applied to thehead, the rotational speed of the disk, and so on. However, since thedistance by which the head floats up must be reduced due to the increasein the recording density of the disk unit (it is ideal that the head islocated as close to the magnetic film as possible), as stated above, andsince the degree at which the protrusions deform and the degree at whichthe protrusions wear must be reduced, the height of the protrusions mustbe made uniform, and the area of the protrusions with which the headsliding surface makes contact must thereby be increased. Furthermore,deep pits must be provided in order to eliminate the debris of thesurface of the disk.

Accordingly, it has conventionally been proposed to make the height ofthe protrusions formed as a consequence of formation of grooves uniformby dividing the polishing process subjected to the surface of the disksubstrate into first and second processes and by polishing theprotrusions in the second process. However, the optimal surfacecharacter of the disk substrate which is subjected to the textureprocess to the CSS characteristics and the head stickiness when theamount at which the head floats up is small, are unknown, and theproblems involving the head crashing or the like have not yet beensolved. More specifically, when the surface of the disk substrate issufficiently polished to make the height of the protrusions uniform, thearea of the surface of the disk against which the head slides (strictlyspeaking, the polished surface of the protrusions with which the headsliding surface makes contact) increases, thereby deteriorating thefloating characteristics of the head. Furthermore, the lubricant coatedon the surface of the disk (generally, a lubricant film is coated on thedisk) or water contents contained in the air may attach to andaccumulate on the head sliding surface due to the surface tension, andmakes the head sliding surface adsorbed to the surface of the disk,causing cessation of rotation of the disk or damage to the head.

Japanese Patent Unexamined Publication No. 62-236664 discloses anothermethod of forming fine irregularities on the recording surface of themagnetic disk. In the conventional methods disclosed by Japanese PatentUnexamined Publications Nos. 54-23294 and 62- 236664 the fineirregularities are formed on the disk substrate 30 in thecircumferential direction by moving the resilient contact rollers 8 backand forth in the radial direction of the disk substrate 30 whilepressing them against the rotating disk 1 through the polishing tapes 4and, concurrently with this, by winding the polishing tapes 4, as shownin FIG. 12. Furthermore, the height of the irregularities is madeuniform by conducting a second process on the surface which has beensubjected to the above-described process as the first process using thepolishing tapes on which abrasive grains having an average graindiameter smaller than that of the polishing tapes employed in the firstprocess are fixed.

The above-described conventional techniques pay no sufficient attentionto the accuracy with which the micro grooves are formed on the recordingsurface and have a disadvantage in that the pitch or height of the fineirregularities on the recording surface differs depending on the site ofthe recording surface. Furthermore, these techniques suffer from aproblem in that the irregularities cannot be formed on the surface ofthe disk at a height or pitch required to satisfy the head flyability tothe disk or the durability of the disk surface due to use of anon-uniform abrasive grains of the polishing tapes. The presentinventors made experiments in which irregularities were formed on aNi--P plated aluminum disk 17 shown in FIG. 9 in the manner shown inFIG. 12 using a polyester film polishing tape 4 to which aluminum oxidegrains having a grain diameter of 3 μm were fixed. The aluminum disk 17had a surface roughness Ra of 2 to 3 nm, an outer diameter of 130 mm, aninner diameter of 40 mm, and a thickness of 2 mm. The experiments wereconducted under a pressurizing force of 10 N, at a disk rotational speedof 400 rpm, at an elastic contact roller feed speed of 100 mm/min, andat a polishing tape feed speed of 100 mm/min. FIG. 43 shows thecross-section of the thus-obtained disk. As shown in FIG. 43, the heightof the protrusions and the depth of the grooves were non-uniform. In thegraph shown in FIG. 43, the axis of abscissa represents the radialdirection of the magnetic disk, and the axis of ordinate represents thevertical direction of the irregularities. When a magnetic disk unitincorporating such a magnetic disk was driven, the magnetic head couldnot float stably and was damaged due to so-called head crash in whichthe magnetic head makes contact with the protrusions on the surface ofthe magnetic disk. Furthermore, when the magnetic head was caused toslide 1000 times against the disk, the lubricant film or the protectivefilm formed on the magnetic disk was broken. Furthermore, the tangentialforce of the magnetic head increased, as shown by the curve 122 of FIG.40, in proportion to the times with which the magnetic head was causedto slide, and reached about 0.1 N and the cessation of rotation of themagnetic disk thereby occurred when the magnetic head caused to slide10,000 times. Hence, the surface of the disk was conventionally madelevel by conducting the second process on the surface of the disk, i.e.,by polishing it again with the polishing tapes 4 of the smaller abrasivegrains. However, even if the protrusions of the very non-uniformirregularities shown in FIG. 43 are polished to some degree by thesecond process, the aforementioned problems remain unsolved.

In addition to the above-described Japanese Patent UnexaminedPublication Nos. 54-23294 and 62-248133, the method of forming a textureby providing fine irregularities on the substrate of the magnetic diskin order to improve durability of the disk surface and electricalcharacteristics is also disclosed in Japanese Patent UnexaminedPublication No. 62-203748. In these texture forming methods, the textureis formed in the circumferential direction of the disk by using thepolishing tape or free abrasive grains. In a case in which the polishingtapes are used, the texture is formed by the conventional diskmanufacturing method shown in FIG. 12 by moving the contact rollers 8back and forth in the radial direction of the disk 2 while pressing themagainst the rotating disk 2 through the polishing tapes 4 and,concurrently with this, by winding the polishing tapes 4. FIG. 55B showsthe cross-section of the surface of the thus-obtained disk, which wasmeasured along the direction indicated by the arrow in FIG. 55A.

However, the aforementioned conventional techniques give no attention tothe accuracy of the shape, and have a problem in that thecross-sectional form of the surface of the disk differs depending on theposition thereon. Furthermore, the above-described conventionaltechniques employ the polishing process and thus surface from problemsin that debris of the surface is generated, in that scratches aregenerated and in that the processing residue remains.

Furthermore, since the aforementioned conventional techniques employabrasive grains in the form of a polishing tape or the like, the heightor pitch of the irregularities of the texture cannot be freely set, andit is therefore difficult to form irregularities that can satisfy thehead floating characteristics, the contact start-stops characteristicsand the electrical characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to eliminate the aforementionedconventional problems.

A primary object of the present invention is to provide a magnetic diskwhich exhibits excellent contact start-stops characteristics and doesnot easily generate head crashing even when the amount at which the headfloats is made smaller in order to achieve improvement in the flyabilitybetween the magnetic disk and head and the durability of disk surface.

A second object of the present invention is to provide a method ofmanufacturing such an improved magnetic disk.

A third object of the present invention is to provide an apparatus formanufacturing the above-described magnetic disk.

A fourth object of the present invention is to provide a magnetic diskunit in which such a magnetic disk and a magnetic head driving deviceare provided as one unit.

In order to achieve the aforementioned objects, the present inventionprovides the following magnetic disk, the method of and apparatus formanufacturing the same, and the magnetic disk and head assembly.

The magnetic disk provided to achieve the first object of the presentinvention includes a non-magnetic substrate with a surface processedlayer having fine irregularities formed at least on a main surfacethereof, and at least a thin film magnetic layer and a protecting layerformed in that order on the non-magnetic substrate in such a manner thatthe fine irregularities are duplicated thereon. The surface processedlayer of the non-magnetic substrate has protrusions whose surfacecharacter is essentially made level, and has a surface configurationwhich exhibits a three-dimensional bearing curve in which a bearingratio at a section taken at a depth from the top of the surface whichcorresponds to the portion deformed by a head load during the CSSoperation is between 0.1 and 10%.

Preferably, the magnetic disk includes a non-magnetic substrate with asurface, processed layer having fine irregularities formed at least on amain surface thereof, and at least a thin film magnetic layer and aprotecting layer formed in that order on the non-magnetic substrate insuch a manner that the fine irregularities are duplicated thereon. Thesurface processed layer of the non-magnetic substrate has surfacecharacteristics of protrusions whose height ranges from several nm toseveral tens of nm and whose surface is essentially made level, and asurface configuration which exhibits a three-dimensional bearing curvein which bearing ratio at a section taken at a depth of 5 to 10 nm fromthe top of the surface of the protrusions is between 0.1 and 10%.

More preferably, the non-magnetic surface processed layer has surfacecharacteristics which exhibit a three-dimensional bearing curve in whicha portion of the curve which represents a surface layer thereof is flat.

More preferably, the non-magnetic substrate surface processed layer hasa surface characteristics in which micro grooves having a depth of atleast 100 nm is present within a length thereof corresponding to thewidth of a head slider sliding surface and in which the symmetry of asectional curve thereof Rsk is equal to or smaller than -0.7.

In order to provide an irregular surface in which micro grooves having auniform height are formed at a uniform pitch over the entire surface ofthe disk, micro grooves are regularly formed with a high degree ofaccuracy on a recording surface of the magnetic disk substrate employinga cylindrical, drum-like, spherical or conical plastic working tool onthe surface of which micro projections are formed.

In order to provide a magnetic disk whose sectional form is uniform,which eliminates residue, and which is highly accurate and reliable,fine irregularities are formed on a magnetic medium film formed on anon-magnetic intermediate film formed on the surface of a substrate.

A magnetic disk manufacturing method which is provided to achieve thesecond object of the present invention includes the steps of forming anirregular processed layer on a specular finished surface of anon-magnetic substrate by conducting first and second polishingprocesses on the specular finished surface of the non-magneticsubstrate, forming a thin film magnetic layer on the irregular processedlayer formed by the polishing processes, and forming a protective filmon the thin film magnetic layer. The first polishing process ischaracterized by the formation of micro projections having apredetermined depth on the substrate at least within a length thereofcorresponding to the width of a sliding surface of a magnetic head. Thesecond polishing process is characterized in that, when protrusionsformed at shoulders of the micro grooves as a consequence of formationof the micro grooves are to be polished to remove a predetermined amountof top portion thereof and thereby made flat, polishing of the topportion is suspended when it is detected in a three-dimensional bearingcurve representing the surface configuration of the irregular processedlayer that a bearing ratio at a section taken at a depth correspondingthe portion deformed by the head load during the CSS drive is between0.1% and 10%.

More specifically, a magnetic disk manufacturing method which isprovided to achieve the second object of the present invention includesthe steps of forming an irregular processed layer on a surface of anon-magnetic substrate by conducting first and second polishingprocesses on the specular finished surface of the non-magneticsubstrate, forming a thin film magnetic layer on the irregular processedlayer formed by the polishing processes, and forming a protective filmon the thin film magnetic layer. The first polishing process ischaracterized by the formation of micro projections having apredetermined deep groove at least within a length corresponding to thewidth of a sliding surface of a magnetic head. The second polishingprocess is characterized in that, when protrusions formed at shouldersof the micro grooves as a consequenc,e of formation of the micro groovesare to be polished to remove a predetermined amount of top portionthereof and made flat, polishing of the top portion is suspended when itis detected in a three-dimensional bearing curve representing thesurface configuration of the irregular processed layer that a bearingratio at a section taken at a depth of 5 to 10 nm from the surface topof the protrusions is between 0.1% and 10%.

More preferably, the first polishing process includes the steps ofprocessing the non-magnetic substrate and washing the processednon-magnetic substrate. The non-magnetic substrate is processed bypressing first polishing tapes against the two surfaces of thenon-magnetic substrate under a predetermined first pressure whilefeeding them in the circumferential direction of the non-magneticsubstrate and vibrating and moving them in the radial direction of thenon-magnetic substrate and, at the same time, by rotating thenon-magnetic substrate at a rotational speed which ensures apredetermined first relative speed with respect to that of the firstpolishing tapes while a processing solution is being supplied to thesurface to be polished. The second polishing process includes the stepsof processing the non-magnetic substrate and washing the processednon-magnetic substrate. The non-magnetic substrate is processed bypressing second polishing tapes of abrasive grains having a grain sizesmaller than that of the first polishing tapes against the two surfacesof the non-magnetic substrate under a predetermined second pressurewhich is smaller than the first pressure while feeding them in thecircumferential direction of the non-magnetic substrate and vibratingand moving them in the radial direction of the non-magnetic substrateand, at the same time, by rotating the non-magnetic substrate at arotational speed which ensures a predetermined second relative speedwith respect to that of the second polishing tapes which is larger thanthe first relative speed while a processing solution is being suppliedto the surface to be polished.

The top portion of the micro grooves formed on the recording surface mayalso be polished by the electro polishing, the lapping polishingemploying a plate on which a polisher is adhered and abrasive grainsliquid, or the lapping polishing in which a polishing tape is pressedthrough an elastic roller or pneumatically.

The micro grooves may be copied on the recording surface of a plasticmagnetic disk substrate or a magnetic disk substrate with a plasticcoated thereon or a substrate formed of a material that can be processedregularly and with a high degree of accuracy using the magnetic disksubstrates manufactured by the above-described method as an originalsubstrate.

The magnetic disk may also be manufactured by forming fineirregularities on the surface of the substrate thereof by means of theplastic working and then by coating a non-magnetic film and a magneticmedium film on the substrate.

The magnetic disk may also be manufactured by forming fineirregularities on a non-magnetic film or a magnetic medium film and aprotective film coated on the surface of the substrate of the magneticdisk by means of the plastic working.

The magnetic disk manufacturing apparatus which is provided to achievethe third object of the present invention includes a substratesupporting tool for rotatably supporting a disk substrate, a firstprocessing head having a contact roller unit for simultaneously pressingpolishing tapes used in a first polishing process against the twosurfaces of the substrate, a tape winding roller for winding thepolishing tapes, and a reciprocatively moving means for vibrating thecontact roller unit in the radial direction of the substrate, a secondprocessing head disposed on the opposite side of the substratesupporting tool for conducting a second polishing process, the secondprocessing head having the same configuration as that of the firstprocessing head, a substrate rotating means for rotating the substratesuch that the speed thereof relative to the polishin9 tapes is apredetermined value, a substrate washin9 means disposed between the twoprocessing heads for washin9 the substrate, and a control unit forcontrolling at least an operation timing of the two processing heads andthe substrate rotation means.

The magnetic disk manufacturing apparatus according to the presentinvention may also include a means for supporting and rotating a thinfilm magnetic disk, a processing tool comprising a rotary member whoserotary axis lies in the radial direction of the thin film magnetic disk,a surface of the rotary member having fine irregularities, theprocessing tool being capable of plastically working a surface of thethin film magnetic disk, a supporting member on the forward end of whichthe processing tool is rotatably mounted, and a control means fordisplacing the supporting member and thereby controlling a pressurizingforce applied to the thin film magnetic disk by the processing tool.

More specifically, in the magnetic disk manufacturing apparatus, thefine irregularities formed on the surface of the processing tool aretransferred onto the surface of the substrate (for a magnetic disk) madeof, for example, an aluminum alloy, anodic aluminum oxide or an Ni--Pplated aluminum alloy, or on a non-magnetic film or a magnetic mediumfilm formed on the substrate by the sputtering or the plating to form atexture by pressing the processing tool against the surface of therotating disk under a fine and uniform pressure and, at the same time,by moving it back and forth in the radial direction of the disk. Theprocessing tool comprises a rotary member whose central axis lies in theradial direction of the disk. The processing tool has a cylindrical formor the surface of the processing tool with which the disk makes contactis spherical. The surface of the processing tool may be coated bydiamond or TiC. In order to form the configuration of the surface of thedisk with a high degree of accuracy, the processing tool is pressedagainst the surface of the disk under a fine and constant pressure.

A processing tool which has a highly accurate configuration and exhibitsexcellent wear-resistant characteristics may be provided by forming fineirregularities on the surface of a sintered hard alloy by means of thecutting or the dry etching and then by coating diamond or TiC on thesurface of the sintered hard alloy.

The magnetic disk unit which is provided to achieve the fourth object ofthe present invention includes a plurality of magnetic disks mountedcoaxially and separated with a predetermined distance, and a headdriving unit for recording data on and retrieving data from the magneticdisks by a CSS driving method in which a head slider on which a magnetichead is mounted is elastically in contact with and slides against atleast one surface of each of the disks under a predetermined pressure ina state where the disk is stationary and in the initial state ofrotation of the disk, in which the head slider floats up due to therotation of the disk at a high speed, and in which the head slider ismoved back and forth in the radial direction of the disk. The surfacecharacter of the magnetic disk against which the head slider slides hasa configuration which is the duplicate of a surface configuration of anirregularly processed layer on a surface of a magnetic disk substratewhich is a non-magnetic substrate. The surface character of the disksubstrate has protrusions whose surface is made flattened, and exhibitsa three dimensional bearing curve in which a bearing ratio at a sectiontaken at a depth from the top portion of the surface which correspondsto the portion of the surface deformed by the head load during the CSSdrive is between 0.1 and 10%.

Preferably, the surface character of the disk substrate may haveprotrusions whose height is between several nm and several tens of nmand whose surface is made flat, and exhibits a three-dimensional bearingcurve in which a bearing ratio at a section taken at a depth of 5 nm to10 nm from the top of the protrusions is between 0.1% and 10%.

More preferably, the surface character of the disk substrate may exhibita three-dimensional bearing curve in which the portion thereofrepresenting a surface layer is flat. More preferably, the surfacecharacter of the disk substrate may have at least one micro groovehaving a depth of about 100 nm within a length thereof corresponding tothe width of a head slider sliding surface, and exhibit a sectionalcurve whose symmetry is indicated as Rsk≦-0.7. More preferably, if thepressure provided by the head load W received on the area S of the disksurface with which the head slider makes contact is W/S, and if theyield strength of the fine protrusions formed on the surface of the disksubstrate is σ, the disk sliding surface may have an initial state inwhich σ≧W/S holds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are respectively front views of an embodiment of asubstrate processing apparatus according to the present invention;

FIG. 2A is a plan view of the essential parts of the apparatus of FIGS.1A and 1B whose main part is a head;

FIG. 2B is a partial section of FIG. 2A;

FIG. 3 is a front view of a substrate washing means in the apparatus ofFIGS. 1A and 1B;

FIG. 4 is a side elevational view of the substrate washing means;

FIG. 5 is an enlarged graphic representation of a sectional curve of thesurface of the substrate which is processed by a first processing headH1 of the substrate processing apparatus of FIGS. 1A and 1B;

FIG. 6 is an enlarged graphic representation of a sectional curve of thesurface which is processed by a second processing head H2;

FIG. 7 is a front view of a conventional substrate processing apparatusfor forming micro grooves;

FIG. 8 is a side elevational view of the substrate processing apparatusof FIG. 7;

FIG. 9 is a sectional view of a thin film magnetic disk in which asubstrate according to the present invention is employed;

FIG. 10 is a sectional view of a conventional thin film magnetic disk;

FIG. 11 illustrates the sectional form of a micro groove;

FIG. 12 illustrates a conventional substrate processing apparatus;

FIG. 13 shows the relation between the height of fine protrusions andthe head flyability and the head-friction;

FIG. 14 shows the relation between the symmetry and the head flyabilityand the head friction;

FIGS. 15A and 15B respectively show the sectional form of the surface ofthe substrate obtained by measuring fine changes in the surface prior tothe CSS drive and after the CSS drive in the order of nanometer by ahigh-resolution SEM;

FIG. 16 shows three-dimensional bearing curves of the surface layer ofthe substrate which are obtained before and after the CSS drive;

FIGS. 17 and 18 respectively show the sectional form of the surface ofthe magnetic disk on which the substrate according to the presentinvention is formed and of the magnetic disk on which a magnetic mediumin the form of film is formed on the substrate;

FIG. 19 shows the relation between the CSS cycles and thehead-frictions;

FIG. 20 is a perspective view, with parts broken away, of a magneticdisk unit according to the present invention;

FIG. 21 illustrates the relation between a magnetic disk and a magnetichead;

FIG. 22 is a perspective view of a head slider, showing the form of amagnetic head;

FIGS. 23A and 23B respectively show the relation in contact start-stopbetween the head and the surface of the disk obtained when the disk isat a stop and when the disk is rotating.

FIG. 24 illustrates the principle of the method of three-dimensionallymeasuring a texture processed surface by means of the SEM;

FIG. 25 three-dimensionally shows a texture processed surface of amagnetic disk according to the present invention;

FIG. 26 three-dimensionally shows a conventional texture processedsurface;

FIGS. 27A, 27B, 28A and 28B show the relation between thecross-sectional form of the texture processed surface and thethree-dimensional bearing curve thereof;

FIG. 29 shows fine protrusions in the sectional form of the textureprocessed surface;

FIGS. 30A to 31B illustrate the configuration of the texture processedsurface according to the present invention using the three-dimensionalbearing curves;

FIG. 32 shows the relation between the three-dimensional sectionalbearing ratio and the head flyability and the head-friction;

FIG. 33 is a front view of a substrate processing device used to conducta first process of another embodiment of the present invention;

FIGS. 34A and 34B respectively are a general perspective view and apartially enlarged view of the form of a plastic working tool accordingto the present invention employed in the processing device of FIG. 33;

FIG. 35 is a partial plan view of the processing device of FIG. 33;

FIG. 36 is a perspective view, with parts broken away, of a two surfacepolishing device which is used in conducting a second process of anotherembodiment of the present invention;

FIG. 37 is a schematic view of the electro polishing method used toconduct the second process of another embodiment of the presentinvention;

FIG. 38 shows the measured sectional form of a recording surface of amagnetic disk substrate which is subjected to the first process shown inFIG. 33;

FIG. 39 shows the measured sectional form of a recording surface of amagnetic disk substrate which is subjected to the second processemploying the two surface polishing device of FIG. 34;

FIG. 40 shows the results of the magnetic head sliding tests conductedon a magnetic disk according to the present invention and on aconventional magnetic disk as compared;

FIG. 41 shows the measured sectional form of a recording surface of amagnetic disk substrate which is subjected to the second process shownin FIG. 37;

FIG. 42 is a schematic view of another example of a polishing tapepolishing device employed to conduct the second process according to thepresent invention;

FIG. 43 shows the measured sectional form of a recording surface of amagnetic disk substrate which is subjected to the conventional firstprocess;

FIG. 44 shows a method of manufacturing a copying mold from the magneticdisk substrates obtained in the second embodiment of the presentinvention;

FIGS. 45A to 46B are respectively perspective and enlarged views of aprocessing tool employed in another embodiments of the magnetic diskmanufacturing method according to the present invention;

FIGS. 47 and 48 show the relation between the disk processed by theprocessing tools in FIGS. 45A to 46B and the magnetic head;

FIGS. 49A to 51B respective show the direction in which the disk isprocessed by the processing tools shown in FIGS. 45A to 46B and thesectional form of such a disk;

FIG. 52 is an upper plan view of the essential parts of anotherembodiment of a disk manufacturing apparatus according to the presentinvention;

FIG. 53 shows an Abott-Firestone bearing ratio curve of a disk obtainedin Example 3 of the present invention;

FIG. 54 shows an Abott-Firestone bearing ratio curve of a disk obtainedby a conventional disk manufacturing method;

FIGS. 55A and 55B shows the direction in which a disk processed in theconventional disk manufacturing method and the sectional form of thedisk;

FIG. 56 is a perspective view of the contact side of a glass heademployed in a Fizeau interferometer;

FIG. 57 shows an operation output obtained when the head of FIG. 56 islightly brought into contact with the magnetic disk; and

FIGS. 58A and 58B respectively show the sectional forms obtained in thedirection indicated by C in FIG. 57 when no load is applied and when ahead is pressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, the examinations made by the present inventors to create thepresent invention will be described in detail.

The present inventors determined that the shape of the outermost surfaceof the disk changed by the order of one nanometer (nm) because of thesliding of the head slider mounted on the magnetic head against it andthat the surface of the disk was thereby made level, increasing thehorizontal resistance exerted on the head and causing head crashing orhead stickiness when the head was stopped during the CSS (contactstart-stops) operation, which led to cessation of rotation of the head.The present inventors thus found that to specify the maximum surfaceroughness and the height of the protrusions as the processing conditionsof the texture processed surface of the disk substrate was not enough toexplain the CSS characteristics and the durability of disk surface suchas head crashing of the magnetic disk. The present inventors alsonoticed that no consideration was taken of the fact that the overallproperties, including the configuration of the protrusions from theaverage surface and the configuration of the pits, as well as theproperties of the three-dimensional bearing curve, which will bedescribed later, were more important than the maximum surface roughness,and that no specification was therefore presented on the irregularitiesformed on the surface of the substrate which was necessary to improvehead crashing and the CSS characteristics.

FIG. 20 shows part of a magnetic disk unit 85 as a sectioned perspectiveview. The magnetic disk unit 85 includes a plurality of magnetic disks80 which are mounted coaxially and equally spaced, and magnetic heads 81for writing data on and reading data from the corresponding surfaces ofthe disks. FIG. 21 schematically illustrates the relation between thedisk 80 and the head 81 (also called a head slider) in the magnetic diskunit shown in FIG. 20. The head 81 is fixed to the forward end of an arm84, and is respectively in contact with and slides against the surfaceof the disk when the disk is stationary and at the initial stage of therotation of the disk due to the elastic force of the arm 84 appliedthereon. Once the rotational speed of the disk has increased, the head81 floats up to a position separated from the disk by a submicroscopicdistance under the effect of air stream to the disk 80. These states ofthe head are illustrated in FIGS. 23A and 23B. FIG. 23A illustrates thestate in which the head is in contact with the disk which is obtainedwhen the disk is at a stop and when the head slides against the disk,and FIG. 23B illustrates the state in which the head floats up in theair which is obtained when the disk is rotating at a high speed. Asshown in FIG. 22, the head 81 has a slider 82 which slides against thesurface of the disk at each side thereof.

The surface of the head slider 82 has a width of 0.4 mm (w) and a lengthof 4 mm (λ). The head slider 82 is mounted with its longer side beingsubstantially directed in the circumferential direction of the disk.What counts regarding the irregular configuration of the surface of thedisk is hence the irregular configuration with respect to at least awidth w of head sliders i.e. a width of 0.4 mm or above.

The method of measuring the cross-sectional form of the surface of thesubstrate subjected to the texture process will be described now.Measurement was conducted in the radial direction of the substrate overa length corresponding to the width w of the head slider (e.g., 0.4 mm)or above using a surface roughness tester TALY STEP (manufactured byRank Talor Hobson) which employed a stylus having dimensions of 0.1μm×2.5 μm. The cross-sectional form of the surface of the substrate isrepresented by a curve. An output signal from TALY STEP was A/Dconverted, and the obtained digital signal was processed by a computer.The analog signal was sampled at intervals of less than 40 nm.

Fine protrusions represent respective fine crest (called protrusions inthis invention) which protrude from a central line C (FIG. 29) of theabove-described cross-sectional curve obtained by conducting measurementin the radial direction of the substrate on which texture is formed inthe approximately circumferential direction thereof or in a helicalfashion. The height Rp of the fine protrusion represents the distancebetween the central line and the highest crest among the crests locatedwithin a unit length L measured in the radial direction of thesubstrate.

The symmetry of the cross-sectional curve, which is one of the surfacecharacteristics of the texture processed surface, is expressed by Rskobtained in the following equation in accordance with the knownnotation. If the cross-sectional curve is represented by function Y (i),then ##EQU1## where Rq is the surface roughness-root-mean square whichis expressed by ##EQU2##

More specifically, in a case where Rsk representing symetry is anegative value, the sectional curve has a large pit component, and in acase where Rsk is a positive value, the sectional curve has a largeprotrusion component. Rsk=0 means that the ratio of the protrusioncomponent to the pit component is equal and that the cross-sectionalcurve is symmetric with respect to the central line C.

The method of three-dimensionally measuring the irregularities on thetexture processed surface will be described below with reference toFIGS. 30A and 30B. FIG. 30A illustrates the results of thethree-dimensional surface measurement G by means of Scanning TunnelingMicroscope (STM) which will be described later. The three-dimensionalsurface is cut along an equally spaced plane H (whose depth from theoutermost surface is Δhi) which is parallel to the average surface, andthe area ratio obtained by dividing the area of the three-dimensionalform at each section by the overall area thereof at a referentialsurface E which is located deeper than the irregular processed layer isplotted with respect to each section in the graph shown in FIG. 30B. Inother words, the graph shown in FIG. 30B is a three-dimensionalexpressed bearing curve.

This three-dimensional bearing curve is similar to contents to theAbbott-Firestone (or bearing ratio) curve obtained from thetwo-dimensional cross-sectional curve, as shown in FIGS. 31A and 31B,and is the three-dimensional form thereof. The Abbott-Firestone curve isemployed to estimate the sliding characteristics of, for example, abearing. The present inventors observed and measured the contact of thehead with the disk in terms of the state of the head sliding surface,the state of the disk surface, and motion of the head and disk duringthe CSS operation, and found that the three-dimensional bearing curveobtained by means of the STM is very effective as the method ofestimating the surface of the disk with a high degree of accuracy interms of the sliding characteristics thereof.

More specifically, as shown in FIGS. 30A and 30B, in the bearing curve,the three-dimensional configuration G of the surface is cut along aplane H which is equally spaced from the top of the three-dimensionalconfiguration, and the area ratio (percentage) obtained by dividing thetotal area of the three-dimensional configuration at each section by theoverall area of a referential surface E is plotted for each section. Atthe top portion of the surface configuration, the area of the surfaceconfiguration at the section is small, and the area ratio is thus small.In other words, if the sliding member is located on such a surface, itis supported only by the top portion of the surface configuration at theinitial stage of the sliding. Thus, the pressure receiving area issmall, and the pressure received by the unit pressure receiving area islarge. In consequence, the top portion of the surface configurationeasily wears or deforms by the friction caused by the sliding of thesliding member. In contrast, at the surface where the area ratio of thetop portion of the surface configuration is large, i.e., at the surfaceconfiguration whose gradient of the bearing curve is small in the rangewhere the area ratio is small in the three-dimensional bearing curve,the pressure receiving area is large in the initial stage of thesliding, and the pressure received by the individual fine protrusion tosupport the sliding member is thus small, providing improvedsliding-resistance characteristics. Thus, the three-dimensional bearingcurve is used to estimate the ability with which the surface againstwhich the sliding member slides can receive loads.

The principle of another method of three-dimensionally measuring thetexture processed surface will be described with reference to FIG. 24.This method employs a scanning electron microscope (SEM). The intensityof the signals a and b at an incident angle θ (gradient of a sample) ofan electron probe are respectively detected by two secondary electrondetectors A and B, and θ is obtained from the following general formulaif the signal intensities at the incident angle of 0 (which means thatthe electrons are incident onto a flat plane) are an and bn.

    tan θ=k{(a.sup.2 -b.sup.2)/(an+bn).sup.2 }

(where k is a constant) The thus-obtained gradients of the sample areintegrated to obtain the surface configuration in the direction of Xaxis. An electron rays surface configuration analyzing device,manufactured by ELIONIX, may be employed as the measuring device.

The three-dimensional surface configuration can be measured by scanningthe sample in the direction of Y axis.

The three-dimensional bearing ratio can also be estimated by employingthe principle of optical interference. In this method, the surfaceconfiguration of the substrate of a magnetic disk is measured when noload is applied thereto and when a load is applied thereto using atransparent glass head 170 mounted on a load applying arm 172 through aplate spring 174 such that it can apply a load to the substrate, asshown in FIG. 56, by means of the piezo interferometer (see page from526 to 533 in "An analyzing device for Fizeau interferometer" 27.9(1989) by Hikari Gijitsu Kontakuto), and the area of the substrate ofthe magnetic disk with which the substrate is in contact with the headwhen loads are applied is operated and indicated in the manner shown inFIG. 57. In that case, the overall measurement range is 5.5×5.5 mm, andthe resolution on a horizontal plane is 10.9 μm. FIG. 58A is a graphicrepresentation of changes in the surface configuration which areobtained by measuring the surface A in the direction indicated by thearrow C of FIG. 57 when no load is applied thereto, and FIG. 58B is agraphic representation of changes in the surface configuration obtainedby the same measurement when loads are applied.

This method is capable of measuring changes in the vertical direction inthe area corresponding to the dimension of the magnetic head (e.g., 3×4mm), the real area of contact between the head and the disk obtained ina state when the head load is applied, the state in which the contactarea increases as the head load increases, and changes in the contactstate between the head and the disk which are obtained in the process inwhich the surface of the disk changes as the start-stop-cyclesincreases.

The present invention which is devised on the basis of theabove-described knowledge will be described more concretely below.

The substrate of the magnetic disk is made of an aluminum alloy, anodicaluminum oxide, an aluminum alloy plated with Ni--P, glass or a plastic.In order to improve the characteristics, it is required that the surfaceof the substrate have a large number of uniform micro grooves and fineprotrusions.

These micro grooves and fine protrusions are formed on the surface ofthe substrate by means of a polishing tool such as a diamond bite orfine abrasive grains, and the fine protrusions are formed at theshoulders of the micro grooves as a consequence of formation of themicro grooves as the rising portions 36 shown in FIG. 11, as statedabove. The height of the fine protrusion is determined by the depth orsize of the pit 37, and the number of micro projections is determined bythe processing conditions including the density of the fine abrasivegrains or the tool feeding.

The requirements of the surface characteristics of the magnetic disk areto satisfy the various types of characteristics of the magnetic disk,including the electrical characteristics, the CSS characteristics andthe head-stickiness characteristics, without causing head crashing. Thegap between the floating head and the disk is reduced in order toachieve high-density magnetic disks. So, it is required that the surfaceof the disk is made high-smooth to avoid oollision of the head aqainstthe disk. From the viewpoint of reduction in the head access time,so-called contact-start-stop (hereinafter referred to as a CSS) isconducted on the head 81 and the disk 80, as shown in FIGS. 23A and 23B,in which the head 81 is in contact with the disk 80 when it is at a stopand in which the head floats up while the disk is rotating. Inconsequence, in a case where the surface of the disk 80 has a smoothsurface, i.e., the surface has a very small surface roughness, headadhesion occurs while the head is at a stop due to the lubricant 83coated on the surface of the disk or the water contents in the air,damaging the gimbal or the arm which supports the head or causingcessation of rotation of the head. FIGS. 13, 14 and 32 respectively showthe results of the experiments made by the present inventors, i.e., therelation between the height of the fine protrusions formed on thesubstrate using the polishing tapes by means of the texture process(which will be described in detail later) and the head floatingcharacteristics and the head-stickiness, the relation between thesymmetry of the cross-sectional curve of the texture processed surfaceand the head floating characteristics and the head-stickiness force, andthe relation between the three-dimensional bearing ratio and the headfloating characteristics and the head-stickiness.

More specifically, FIG. 13 shows the relation between the height of theprotrusions and the head floating position HtO which represents thefloating characteristics and the head-friction Ft which is the barometerof the head-stickiness, FIG. 14 shows the relation between the symmetryRsk and the Hto and Ft, and FIG. 32 shows the relation between thethree-dimensional bearing ratio (at the section which is 5 nm deep fromthe topmost portion) and Hto and Ft. The head floating position Hto andthe head-friction Ft are measured as follows:

(i) Measurement of head floating position Hto

A magnetic disk unit having the same structure as that of the disk unitshown in FIG. 20 is employed. An acoustic emission (AE) or Piezo sensoris mounted on the head 81 beforehand. As the disk 80 starts rotating,the head 81 starts floating. The state at that time in which the disk isin contact with the head is detected by the AE sensor. The rotationalspeed of the disk at which the output signal from the AE sensor suddenlydrops is measured.

The head floating characteristics at various rotational speeds of thehead are examined beforehand, and the head floating position Hto isobtained from those head floating characteristics.

(ii) Measurement of head-friction Ft

The head sliding resistance at 1 rpm is measured by a strain gagemounted on the supporting arm 84 of the head 81.

From the results of the experiments, it can be seen that there existsthe effective range of the conditions of the surface characteristicsthat can satisfy both the head floating characteristics and thehead-friction, i.e., in which the floating position Hto is small and inwhich the head-friction Ft is small. More specifically, it can be seenthat the floating position Hto is small and the tangential force Ft issmall when the height Rp of the fine protrusions is between several nmand several tens of nm, and more preferably, in the range indicated bythe arrow in FIG. 13, when the symmetry Rsk shown in FIG. 14 isnegative, more preferably, in the range of Rsk≦-0.7 which is indicatedby the arrow in FIG. 14, and when the three-dimensional cross-sectionbearing ratio is between 0.1 and 10%, and more preferably, between 0.24and 8.5%. As shown in FIG. 32, the effective lower limit of the bearingratio is determined by the floating characteristics, whereas theeffective upper limit of the load ratio is determined by the headstickiness (represented by the head tangential force Ft).

The relation between the surface characteristics and the CSScharacteristics will further be described with reference to FIGS. 27A to28B.

FIG. 27A shows the cross-sectional form of the surface of the substratesubjected to the texture process using the fine abrasive grains, inwhich the height of the fine protrusions is varied to a large extent.

FIG. 27B shows the three-dimensional bearing curve of this textureprocessed surface. The gradient of this bearing curve is large in therange in which the cross-sectional area ratio is small, i.e., in therange A in FIG. 27B. When the CSS drive is repeatedly conducted on thesurface shown in FIG. 27A, since the area of the fine protrusions withwhich the head slider makes contact is small and the surface pressureW/S (W: head loads, S: the real area of contact between the head sliderand the disk) is thus large, the surface of the substrate wears ordeforms to a large extent, greatly damaging the lubricating film havinga thickness of several nm and the protective film having a thickness ofseveral tens of nm, which are formed on the substrate in which the fineprotrusions are formed. Wear or deformation of the fine protrusionscaused by the CSS drive is great when the yield strength σ is smallerthan W/S. When the yield strength σ is equal to or larger than W/S, thewear or deformation is low. Assuming that the fine protrusions has wornor deformed by the CSS drive and that the real area of contact hasthereby increased to an extent which satisfies σ≧W/S, and that theprotective film and the lubricant film remain in a complete form, wearor deformation of the fine protrusions would be substantiallyeliminated, and stable surface would be provided. Hence, the surface ofthe substrate having the cross-sectional form shown in FIG. 27A isfurther processed to make the fine protrusions smooth, as shown in FIG.28A. In FIG. 28A, the shape of the flattened fine protrusions isgeneralized as trapezoidal. When the real area of contact between thehead slider and the disk surface is increased until it has aconfiguration which ensures σ≧W/S in the initial state, the surfacepressure of the fine protrusions is reduced, substantially eliminatingwear or deformation of the fine protrusions. This results in theprovision of a stable and highly reliable surface of the magnetic disk.FIG. 28B shows the three-dimensional bearing curve of the surfaceconfiguration shown in FIG. 28A. It can be seen in FIG. 28B that thegradient of the portion A of the bearing curve which represents thesurface layer is very small.

The portion of the conventional texture processed surface having thesurface configuration shown in FIG. 27A which corresponds to the surfaceof the head slider (having dimensions of, for example, 0.4 mm×0.4 mm)exhibits the three-dimensional bearing curve in which the sectional arearatio at a section taken at a depth of 5 nm to 10 nm from the top of thesurface configuration is 0.1% or less. The present inventors conductedthe CSS drive on the magnetic disk having such a substrate, and foundthat head crashing occurred when the magnetic disk was driven 2000 timesor less. The surface shown in FIG. 28A exhibits a three-dimensionalbearing curve in which the sectional area ratio at a section taken at adepth of 5 nm to 10 nm is between 0.1% to 10%. The present inventorsperformed the start-stop-cycles on the magnetic disk having thesubstrate surface shown in FIG. 28A, more than 20000 times, and foundthat both the protective film and the lubricant film maintained theirfunctions and the surface of the substrate was in a stable condition.

Also, the present inventors intensively examined changes in the surfaceof the magnetic disk caused by the CSS drive. The present inventorsperformed the CSS test on the texture processed surface, and found that,as the magnetic head was repeatedly caused to slide against the topportion of the fine protrusions, the top portion was made flat and thearea of the fine protrusions with which the head makes contactincreased, as shown in FIGS. 15A and 15B which show the results obtainedby the SEM observations on the surface of the disk and in FIG. 16 whichshows the three-dimensional bearing curves of the surface layer of thedisk. More specifically, FIG. 15A shows the initial surfaceconfiguration, and FIG. 15B shows the state of the surface whichdeformed after the head was repeatedly caused to slide against it. Thebearing curve B in FIG. 16 represents the characteristics of the surfacelayer shown in FIG. 15A, and the bearing curve A in FIG. 16 representsthe characteristics of the surface layer shown in FIG. 15B on whichsliding was repeatedly conducted. After the start-stop-cycles wasconducted on the surface 20000 times, the top portion of the protrusionshaving a height of 5 to 10 nm changed as a consequence of contact withthe slider surface of the magnetic head, as shown in portion A in FIG.15B. As shown in FIG. 16 which shows the three-dimensional bearingcurves representing the surface of the disk, as the top portion of thefine protrusions having a height of 5 to 10 nm changed, the area ratioat the section of the surface of the disk with which the magnetic headis made contact is increased to 0.1% to several percent. Furthermore,when the height of the fine protrusions was several tens of nm or above,the magnetic head floating characteristics deteriorated, and headcrashing easily occurred. Even though the height of the fine protrusionswas 5 nm or less, when the cross-sectional area ratio was small, thesurface of the substrate which supported the loads of the head duringthe CSS test, i.e., the area of the fine protrusions on which the loadswere applied, was small, and the fine protrusions were thus flattenedimmediately according to the start-stop-cycles. As a result, thehead-friction increased, and head crashing easily occurred.

Furthermore, when the load area of the fine protrusions was small, thepressure received by the individual fine protrusions was large, and thefine protrusions were thus easily flattened or wore. As a result, thelubricant layer and the protective layer, formed to a thickness ofseveral nm on the surface of the substrate, were easily damaged.Furthermore, when the sectional area ratio was 10% or above and the loadarea was thus large, changes in the fine protrusions on the substratecaused by the magnetic head were less. However, head adhesion easilyoccurred by means of the lubricant or the water contents in the air dueto the large contact area. Furthermore, sliding resistance of themagnetic head increased during the CSS drive, and the gimbal or arm ofthe magnetic head was thereby damaged and rotation of the disk wasdifficult.

Thus, in terms of the head floating characteristics and changes in thesurface character due to the head load and the friction generated by thesliding head, it is preferable that the height of the fine protrusionsformed on the texture processed surface of the substrate is betweenseveral nm and several tens of nm, that the roughness Ra of the textureprocessed surface is between several nm and several tens of nm, that thesymmetry Rsk of the sectional curve of the texture processed surface isnegative, preferably, -0.7 or less, and more preferably, -1 or less, andthat, in the three-dimensional bearing curve of the texture processedsurface, the sectional area ratio at the section corresponding to theportion which is deformed by the head load during the CSS drive, i.e.,at the section taken at a depth of 5 to 10 nm from the top portion, isbetween 0.1% and 10%.

From the above-described viewpoints, the optimal surface of thesubstrate of the magnetic disk is defined as follows: in thecross-sectional form of the texture processed surface of the substratein which micro projections are formed in the pseudo-circumferentialdirection thereof, as shown in FIG. 6, the height of the fineprotrusions is between several nm and several tens of nm and is uniform,the surface roughness Ra is several nm and several tens of nm(preferably, between 2 nm and 9 nm), the symmetry Rsk of thecross-sectional curve is equal to or less than -1 and the sectional arearatio at a section taken at a depth of 5 to 10 nm from the top of thesurface is between 0.1% and 10%.

Furthermore, in order to maintain smooth sliding of the head against thedisk, the texture processed surface of the disk must have deep grooves Vwithin the unit width which is the width of the slider, as shown in FIG.6. The depth of the deep grooves V is preferably 100 nm.

The surface of the disk, which has fine protrusions whose height isbetween several nm and several tens of nm, whose roughness Ra is betweenseveral nm and several tens of nm, which exhibits a cross-sectionalcurve whose symmetry Rsk is -0.7 or less, more preferably, -1 or less,and which exhibits a three-dimensional bearing curve in which thesectional area ratio at the section corresponding to the portion whichis deformed by the head load during the CSS drive, i.e., at a sectiontaken at a depth of 5 to 10 nm from the top of the surface, is between0.1% and 10%, has the following advantages: it can receive a desirablehead load when it makes contact with the surface of the slider of thehead during the CSS drive. The lubricant film coated on the surface ofthe magnetic disk can be maintained and adhesion of the magnetic headcan be prevented by means of the irregularities formed in the surface ofthe disk. The debris generated by the sliding of the head can beeliminated by means of the deep pits in the surface of the disk.Furthermore, since a large number of fine protrusions make contact withthe surface of the head slider and since the sectional area ratio at adepth of preferably 5 to 10 nm from the top of the fine protrusions, inwhich deformation occurs due to sliding of the head, is between 0.1% and10%, the pressure received by the respective fine protrusions is small,and changes in the fine protrusions caused by repeating the CSS drive,i.e., deformation or wear thereof, is thus less. This enables theinitial surface character to be maintained. Furthermore, since theheight of the fine protrusions is between several nm and several tens ofnm, which is very small as compared with the gap between the floatingmagnetic head and the surface of the disk (obtained in a normal state)of 80 to 250 nm, even if the magnetic disk assembly accuracy, therotational accuracy of the magnetic disk and variations in the floatingof the magnetic head are taken into consideration, the magnetic head canbe caused to float up with enough space between the head and the topportion of the fine protrusions. This eliminates head crashing.

In consequence, the magnetic disk according to the present invention hassubstantially no wear or damage on the protective film and the lubricantfilm formed to the thickness of several nm on the surface thereof, hasno head adhesion, eliminates an increase in the head-friction caused byrepeatedly conducting the CSS drive, and therefore exhibits excellenthead floatinq characteristics and durability of disk surface and is highreliable.

Embodiments of the present invention will now be described concretely.

An aluminum alloy plate having an inner diameter of 40 mm and an outerdiameter of 130 mm was used as the disk substrate. The two surfaces ofthe aluminum alloy plate were Ni--P plated to a thickness of 10 μm, andthe plated surfaces were then polished to a surface roughness Ra of 2 to3 nm or less. Thereafter, the plated surfaces were further polishedusing the polishing tapes such that they exhibited a cross-sectionalform shown in FIG. 17 in which the height of the fine protrusions formedat the shoulders of the micro grooves was between several nm and severaltens of nm and was uniform, in which the surface roughness Ra wasbetween 5 and 8 nm, and in which the symmetry Rsk of the sectional curvewas between -1 and -2. The cross-sectional form shown in FIG. 17 wasobtained by measuring the surface of the disk in the directionperpendicular to the direction in which the grooves were formed usingthe surface roughness tester TALY STEP whose tracer had dimensions of0.1 μm×2.5 μm. The method of manufacturing such a disk substrate will bedescribed later.

Subsequently, the Cr type non-magnetic metal film 31 and the Co--Ni typemagnetic film medium 32 were formed in sequence to thicknesses of about300 nm and about 60 nm, respectively, on the substrate of the disk bythe sputtering technique, as shown in FIG. 9. Thereafter, the carbonprotective film 33 having the thickness of about 50 nm and the lubricantfilm 34 were formed in sequence.

The surface configuration of the thus-manufactured magnetic disk wasalmost the same as that of the disk substrate shown in FIG. 17, as shownin FIG. 18. That is, the surface roughness Ra of the surface of themagnetic disk was 5.5 nm (while that of the substrate was 5.3 nm), theheight Rp of the fine protrusions was 19 nm (while that of the substratewas 20 nm), and the symmetry Rsk of the cross-sectional form was almostthe same as that of the substrate.

A plurality of such magnetic disks were incorporated in a magnetic diskunit in the same manner as that in which the disks were incorporated inthe magnetic disk unit shown in FIG. 20, with a floating gap of 0.13 μm.No contact of the head with the surface of the disk was detected, andthe disk exhibited the excellent floating characteristics. Furthermore,substantially no change in the surface configuration of the magneticdisk occurred as the start-stop-cycles was advanced.

FIG. 19 is a characteristic curve showing the relation between thestart-stop-cycles and the head-friction (in unit of newton) obtained inthe present embodiment and that of the conventional disk. Acharacteristic curve C indicates the relation obtained in the presentembodiment, and a characteristic curve D indicates that of thecomparison example. As seen from the graph in FIG. 19, in the case ofthe present embodiment, there was substantially no increase in thehead-friction and no head adhesion occurred when the start-stop-cyclewas conducted 30,000 times. It was therefore possible to greatly improvethe reliability of the magnetic disk and that of the magnetic disk unit.

In the magnetic disk in which the substrate formed by the conventionaltechnique had micro grooves of a cross-sectional form shown in FIG. 5and exhibited the characteristic curve D shown in FIG. 19, thehead-friction D increased and damage to the magnetic head and headcrashing occurred as the start-stop-cycles advanced. Furthermore, thecross-sectional form of the surface of the disk greatly changed whenstart-stop-cycle were repeated.

The method of manufacturing the substrate of this embodiment will bedescribed below.

A Ni--P plated film is formed on the two surfaces of an aluminum alloydisk substrate to a thickness of 10 μm by the electroless platingtechnique, and the plated surfaces are then polished until they have asurface roughness Rmax of 0.01 μm to make them smooth. Next, a firstpolishing process, which employs a polishing tape to which aluminaabrasive grains having a grain size of #3000 are fixed is conducted onthe Ni--P plated surfaces of the substrate to form micro 9rooves in theNi--P plated surfaces of the substrate.

Such a surface processing method is described in, for example, JapanesePatent Unexamined Publication No. 54-23294. In this method, microprojections are formed in the two surfaces of the substrate in anapproximately circumferential direction thereof or in a helical fashionby pressing the polishing tapes 4 against the two surfaces of thesubstrate 30 by means of the contact rollers 8 and by moving thepolishing tapes back and forth along the surfaces of the substrate sothat they can slide against the overall surfaces of the substrate whilewinding around the reels 6.

On the surfaces of the substrate which are subjected to theabove-described surface process, abnormal fine protrusions having aheight of 100 nm or above are present at the shoulders of the deep pits.These may cause deterioration in the head floating characteristics andthe head crashing accidents. Consequently, a second polishing process,which employs a polishing tape whose grain size is smaller than that ofthe polishing tape employed in the first polishing process, is conductedin a similar manner on the surfaces of the substrate. As the result ofthis second polishing process, the abnormal height of the fineprotrusions is reduced, and the top portions of the large number of fineprotrusions are made flat, resulting in the provision of a surface shownin FIG. 6 in which the fine protrusions H are made flat and in whichdeep pits V are present in predetermined intervals.

Between the first and second polishing processes, a surface cleaningprocess of the substrate is conducted to remove dirt such as debrisgenerated by the first polishing process. The end of the secondpolishing process is detected on the basis of the three-dimensionalbearing curve obtained on the basis of the principle of the SEM shown inFIG. 24. The second polishing process is ended at a point on the bearingcurve obtained by means of the STM shown in FIG. 30 at which thecondition that sectional area ratio at the section taken at a depth of 5to 10 nm from the top of the fine protrusions is between 0.1% and 10% issatisfied.

Next, an example of an apparatus for texture processing the surface ofthe disk substrate, which is suitably employed when the magnetic diskaccording to the present invention is manufactured, will be described.

First, the structure of the texture processing apparatus will bedescribed with reference to FIGS. 1A, 1B, 2A, 2B, 3 and 4. FIGS. 1A and1B are front views of an example of the apparatus for texture processingthe surface of the substrate, FIGS. 2A and 2B are plan views of theessential parts of the apparatus of FIGS. 1A and 1B, FIG. 3 is a frontview of a substrate washing means in the apparatus of FIGS. 1A and 1B,and FIG. 4 is a side elevational view of the substrate washing means.

Referring first to FIG. 1A, the substrate processing apparatus includesa substrate supporting tool 1 for rotatably supporting a substrate 2 tobe processed, a pair of processing heads H1 and H2, a substrate drivingmotor 3 for rotating the substrate 2 at a speed which ensures that thesubstrate 2 is rotated at predetermined speeds relative to first andsecond polishing tapes employed in the processing heads, a substratewashing means S disposed between the two processing heads for washingthe substrate, and a control unit 17 for controlling the two processingheads H1 and H2, the substrate driving motor 3 and the substrate washingmeans S. The pair of processing heads consists of a first processinghead H1 disposed on one side of the substrate supporting tool, and asecond processing head H2 disposed on the other side of the substratesupporting tool. The first processing head H1 includes a pair of contactroller units C for concurrently pressing first polishing tapes 4 againstthe two surfaces of the substrate 2 under a predetermined pressure, atape winding motor 7a for winding the first polishing tapes 4, avibration means W for vibrating the contact roller units C in the radialdirection of the substrate 2, and a reciprocatively moving means R formoving the contact roller units C back and forth in the radial directionof the substrate 2. The second processing head H2 has the sameconfiguration as that of the first processing head H1 with the exceptionthat it employs second polishing tapes having a smaller grain size.

FIG. 1B is an enlarged view of the essential parts of the apparatusshown in FIG. 1A whose major component is the first processing head H1.

Now, the processing head H1 will be detailed with reference to FIG. 2Awhich is an enlarged plan view of the essential parts thereof and FIG.2B which is a plan view of the essential parts thereof (with part beingbroken). The first processing head H1 includes a pair of parallel platesprings 10 and 11 supported on the reciprocatively moving means R insuch a manner as to be movable in the axial direction of the substrate2. A pressurizing and moving means 23 is provided for moving theparallel plate springs 10 and 11 such that effects of the back tensiongenerated by winding the polishing tapes 4 can be eliminated and suchthat a predetermined fine pressurizing force can be set. A pressurizingforce correcting means 50 (e.g., a piezoelectric actuator) forcorrecting small variations in the pressurizing force resulting from theaccuracy of the configuration of the substrate during the processing ofthe substrate. Contact rollers 8 and 9 are respectively mounted on theparallel plate springs 10 and 11, the contact rollers 8 and 9 beingprovided on the two sides of the substrate 2 with their central axesdirected in the radial direction of the substrate 2. A polishing tapedriving unit 7 is mounted on the reciprocatively moving means R forcausing the polishing tapes 4 to slide between the substrate 2 and thecontact rollers 8 and 9. Stress measuring means 12 and 13 arerespectively mounted on the parallel plate springs 10 and 11, and thecontrol unit 17 is provided for controlling the pressurizing and movingmeans 23 and the pressurizing force correcting means 50 in accordancewith the output of the stress measuring means.

In consequence, in the above-described substrate processing apparatus,small variations in the pressurizing force of the contact roller, whichare caused by variations in the back tension occurring during thewinding of the polishing tape, i.e., small variations in thepressurizing force, which are caused by variations in the tension of thetape occurring as the diameter of the polishing tape wound around thereels 5 and 6 changes, are measured by the stress measuring means 12,and the parallel plate spring 10 is moved by the pressurizing and movingmeans 23 in accordance with the obtained variations so as to keep thepressurizing force of the contact roller 8 against the substrate 2constant regardless of the variations in the tension of the polishingtape. Furthermore, variations in the pressurizing force, caused by thewaviness of the substrate in the circumferential direction thereof or bythe warpage of the substrate in the radial direction thereof, can becorrected by the pressurizing force correcting means 50 which may be apiezoelectric actuator. With the above-described functions, the microgrooves can be formed on the surface of the substrate with a high degreeof accuracy.

The first processing head H1 is disposed on one side of the substratesupporting tool 1 (on the right side as viewed in FIGS. 1A) forconducting the first polishing process on the two surfaces of thesubstrate 2 and thereby forming micro grooves (having a depth of, forexample, about 0.1 μm). The processing head H1 includes tape windingmotors 7a and 7b for winding the first polishing tapes 4 mounted on thetwo contact roller units C disposed on the two sides of the substrate 2in an upward direction, the vibration means W for vibrating the contactroller units C in the radial direction of the substrate 2, and thereciprocatively moving means R for reciprocatively moving the contactroller units C in the radial direction of the substrate 2. Each of thecontact roller units C includes a contact roller 8 for pressing thefirst polishing tape 4 against the substrate 2, and a pressurizing motor14 for applying a predetermined pressurizing force to the contact roller8 through the parallel plate spring 10. The parallel plate spring 10 isprovided with the strain gage 12 for detecting the pressurizing force.The pressurizing motor 14 is adapted to apply the pressurizing force bydisplacing the parallel plate spring 10 in the direction perpendicularto the surface of the substrate 2. The pressurizing force correctingpiezoelectric actuator 50 is adapted to correct fine variations in thepressurizing force with excellent response during the processing of thesubstrate. The vibration means W includes a motor 16, and a crank 55 forconnecting the shaft of the motor 16 and the first processing head H1.The reciprocatively moving means R is capable of transmitting therotation of a motor 15 to the first processing head H1 and therebymoving the processing head back and forth.

The second processing head H2 has the same configuration as that of thefirst processing head H1 with the exception that it employs the secondpolishing tapes in place of the first polishing tapes. The secondprocessing head H2 is disposed on the other side of the substratesupporting tool (on the left side as viewed in FIG. 1A) for conductingthe second polishing process in which the fine protrusions formed by thefirst processing head as a consequence of formation of the micro groovesare removed.

The processing head will be described further with reference to FIGS. 1Aand 1B. A reference numeral 1 denotes a horizontal rotary shaft on whichthe substrate is mounted; 2, a substrate to be processed; 3, a drivingmotor for rotating the rotary shaft 1; 21, a rotatably supported screw;15, a motor for rotating the screw 21, and 22, a reciprocatively movingbase 22 supported in such a manner as to be movable in the radialdirection of the substrate, i.e., in the direction indicated by thearrow A. The reciprocatively moving base 22 has a female screw whichmeshes the screw 21. The screw 21 and the motor 15 in combination formthe reciprocatively moving means R. A reference numeral 23 denotes amoving base supported on the reciprocatively moving base 22 in such amanner as to be movable in the direction indicated by the arrow A, and16, a vibrating unit fixed to the reciprocatively moving base 22 forvibrating the moving base 23 with fine amplitude.

Turning to FIGS. 2A and 2B, a reference numeral 24 denotes a screwrotatably supported on the moving base 23; 14, a pressurizing motor forrotating the screw 24; and 10 and 11, a pair of parallel plate springssupported on the moving base 23 in such a manner as to be movable in theaxial direction of the substrate, i.e., in the direction indicated bythe arrow B. A supporting base 51 of the parallel plate springs 10 and11 has a female screw which meshes the screw 24. The screw 24 and themotor 14 in combination form the pressurizing and moving means. Thereoccur variations in the pressurizing force during the processing whenthere exists on the substrate a waviness in the circumferentialdirection or a warpage in the radial direction. Hence, the parallelplate springs 10 and 11 are mounted on the supporting base 51 providedwith the pressurizing force correcting piezoelectric actuator 50, andthe female screw of the supporting base 51 is in engagement with thescrew 24, as stated above. Reference numerals 8 and 9 denote contactrollers rotatably mounted on the parallel plate springs 10 and 11,respectively. The contact rollers 8 and 9 are provided on the two sidesof the substrate 2 with their axes directed in the radial direction ofthe substrate 2. Reference numerals 18a and 18b denote braking torquemotors mounted on the moving base 23; 5a and 5b, supply reels mounted onthe output shafts of the motors 18a and 18b; 7a and 7b, winding motorsmounted on the moving base 23; 6a and 6b, winding reels mounted on theoutput shafts of the motors 7a and 7b, and 4a and 4b, polishing tapeswhose two ends are respectively fixed to the supply reels 5a and 5b andthe winding reels 6a and 6b. Each of the polishing tapes 4a and 4b iscomposed of a substrate which may be a polyester film, and fine abrasivegrains such as diamond or alumina grains which are held together andadhered to the substrate by means of a binder which may be a resin. Themotors 18a and 18b, the supply reels 5a and 5b, the motors 7a and 7b,and the winding reels 6a and 6b in combination form the polishing tapedriving unit which causes the polishing tapes 4a and 4b to pass betweenthe substrate 2 and the contact rollers 8 and 9. Reference numerals 12and 13 denote the strain gages respectively mounted on the parallelplate springs 10 and 11, and a reference numeral 17 denotes the controlunit for controlling the motors 3, 14, 15 and so on. The control unit 17controls the motor 14 for moving the parallel plate springs 10 and 11and the pressurizing force correcting piezoelectric actuator inaccordance with the outputs of the strain gages 12 and 13.

The substrate washing means S shown in FIG. 1A will now be describedconcretely with reference to FIGS. 3 and 4 which are respectively frontand side elevational views of the essential parts thereof.

The substrate washing means includes a rotary scrubber (which may be abrush or a sponge) 61 for concurrently washing the two sides of thesubstrate, a scrubber driving motor M for rotating the rotary scrubber61, an air cylinder (not shown) for moving the rotary scrubber 61between the position 61' indicated by the broken line and that indicatedby the solid line, and a liquid tank 65. A reference numeral 60 denotesa supply unit for supplying a processing liquid and a washing liquid.

The operation of the thus-arranged texture processing apparatus will bedescribed below.

First, the substrate 2 is mounted on the substrate supporting tool 1 ofthe processing apparatus shown in FIG. 1A. Next, the processingconditions, such as the pressurizing force, the relative speed, thevibration amplitude, and the times at which the control rollers aremoved back and forth are set on the control unit 17.

Next, the substrate processing apparatus is turned on so as to formmicro grooves in the surface of the substrate 2 by means of thepolishing tapes 4a and 4b. Once the substrate processing apparatus ison, the motor 3 rotates the substrate 2, and concurrently with this, thevibrating motor 16 vibrates the first processing head H1 with the presetvibration amplitude while the polishing tape driving unit 7 winds thepolishing tapes 4a and 4b under a fixed pressure, during which thepressurizing force against the substrate 2 is maintained to the firstset pressurizing force. At the same time, the reciprocatively movingmeans R moves the reciprocatively moving base 22 back and forth. Duringthe operation, the rotational speed of the substrate 2 is adjusted bythe substrate driving motor 3 such that the speed of the substrate 2relative to the first polishing tape 4 is maintained to the preset firstrelative speed. During the processing, the processing liquid iscontinuously supplied from the supply unit 60 to the substrate.

Even when the tensions of the polishing tapes 4a and 4b change and theparallel plate springs 10 and 11 are thereby deformed, the control unit17 controls the motor 14 in accordance with the outputs of the straingages 12 and 13, i.e., the amount at which the parallel plate springs 10and 11 are deformed. In consequence, the pressurizing force of thecontact rollers 8 and 9 against the substrate 2 can be maintainedconstant in spite of the variations in the tensions of the polishingtapes 4a and 4b, and the fine pressurizing force can thereby be alwaysmaintained constant. Therefore, fine and uniform micro grooves can befound. Furthermore, variations in the pressurizing force caused by therotation of the substrate 2 and by the sliding of the processing head inthe radial direction of the substrate, i.e., variations in thepressurizing force caused by the waviness on the substrate 2 in itscircumferential direction and by the warpage of the substrate 2 in itsradial direction, can be corrected by the pressurizing force correctingpiezoelectric actuator 50 under the control of the control unit 17.

Once the first processing head has been moved back and forth a presetnumber of times, the processing head H1 retracts (moves rightward asviewed in FIG. 1A), and supply of the processing liquid from the supplyunit 60 stops.

Next, the rotary scrubber 61 located at the position 61' indicated bythe broken line in FIGS. 3 and 4 is moved up to the position 61indicated by the solid line, and the rotary scrubber 61 is then rotatedby the scrubber driving motor M. The substrate 2 is also rotated, andthe washing liquid is supplied from the supply unit 60 to the rotatingsubstrate 2 to wash it. Once the washing operation is completed, therotary scrubber 61 moves down to the position 61' indicated by thebroken line, and supply of the washing liquid stops.

Thereafter, the second processing head H2, disposed on the opposite sideof the substrate supporting tool 1 to the first processing head H1, asshown in FIG. 1A, advances so as to conduct on the substrate 2 thesecond polishing process in which the substrate 2 is processed by meansof the second processing head. During the second polishing process, thesubstrate is rotated by the motor 3, and concurrently with this, thesecond processing head H2 is vibrated at the preset vibration amplitudeby the vibration motor 16 while the polishing tapes 62a and 62b arewound under a predetermined pressure by the polishing tape driving unit7. During the winding of the tapes, the pressurizing force applied tothe substrate is maintained to the preset second pressurizing force. Atthe same, the reciprocatively moving base 63 is moved back and forth bymeans of the reciprocatively moving means. Then, the fine protrusionspreset on the surface of the substrates 2 are removed and made flat bythe the polishing tape 62a, 62b. During the operation, the rotationalspeed of the substrate 2 is adjusted by the substrate driving motor 3such that the speed of the substrate 2 relative to the second polishingtape is maintained to the preset second relative speed. During theprocessing, the processing liquid is continuously supplied from thesupply unit 60 to the substrate. Once the second processing head H2 hasmoved back and forth preset times, the processing head retracts (movedto the left as viewed in FIGS. 1A and 1B), and supply of processingliquid is stopped. Finally, the substrate 2 is washed by the substratewashing means S in the same manner as that of the preceding washingprocess, and the substrate processing apparatus is then turned off.

Thereafter, the substrate 2 in the surface of which desired microgrooves are formed is removed from the substrate supporting tool 1. Amagnetic disk exhibiting the excellent sliding characteristics isprovided by forming a magnetic medium, a protective film and alubricating film in sequence on such a substrate.

An example of polishing a substrate by means of the aforementionedsubstrate processing apparatus will be explained below with reference toFIGS. 5 and 6. The substrate 2 employed in this example was an Al alloysubstrate whose surface was Ni--P plated to a thickness of about 10 μmand has micro grooves formed therein.

FIG. 5 shows an example of an enlarged cross-sectional curve of thesurface of the substrate which is processed by the first processing headH1 (which is subjected to the first polishing process) of the substrateprocessing apparatus shown in FIG. 1, and FIG. 6 shows an example of anenlarged cross-sectional curve of the surface of the substrate which isfurther processed by the second processing head H2 (which is subjectedto the second polishing process).

The substrate 2 was processed by the first processing head H1 while thewater-soluble cutting liquid was being supplied to the substrate 2. TheAl₂ O₃ abrasive grains of the first polishing tape 4 had a grain size of4 μm, and the first pressurizing force applied during this process was10 N. The first relative speed was 4 m/sec, and the vibration amplitudewas 1 mm. The processed surface of the substrate had micro grooveshaving a depth V of about 100 nm and fine protrusions having a height Hof about 30 nm, as shown in FIG. 5. The height of the protrusions varieda lot. The surface had a roughness Ra of 6 to 7 nm and showed across-sectional curve whose symmetry Rsk was -0.3 and athree-dimensional bearing curve in which the sectional area ratio at thesection taken at a depth of 5 nm from the top portion of the surface was0.1% or less.

After the above-described first polishing process was completed, thesecond polishing process was performed. That is, the surface of thesubstrate 2, which was washed by the pure water, was processed by thesecond processing head H2 while the water-soluble cutting liquid wasbeing supplied to the substrate 2. The Al₂ O₃ abrasive grains of thesecond polishing tape had a grain size of 1 μm, and the secondpressurizing force applied during this process was 4 N. The secondrelative speed was 8 m/sec, and the vibration amplitude was 1 mm. Thedepth V of the micro grooves formed in the surface of the substrate 2was maintained to about 100 nm, and the height H of the protrusions wasreduced to about 10 nm or less, as shown in FIG. 6. The height of theprotrusions varied less. The surface had a roughness Ra of 6 to 7 nm andshowed a cross-sectional curve whose symmetry Rsk was -1.5 and athree-dimensional bearing curve in which the sectional area ratio at thesection taken at a depth of 5 nm from the top portion of the surface was0.8% or less.

As stated above, since the protrusions formed at the shoulders of themicro grooves can be reduced by the second processing head, it ispossible to provide a smooth surface in which the micro grooves have adepth V ranging from 20 nm to 100 nm and the protrusions have a reducedheight H. Furthermore, arbitrary micro grooves can be formed by changingthe processing conditions, such as the grain size or the material of theabrasive grains of the polishing tapes, the times at which the contactrollers are moved back and forth along the substrate, and thepressurizing force.

A thin film magnetic disk 80 can be formed by forming on thethus-obtained substrate 30 a non-magnetic metal film 31, a magneticmedium film 32, a carbon protective film 33 and a lubricating film 34 insequence, as shown in FIG. 9. The resultant magnetic disk 80 hasexcellent heat floating characteristics, and is reliable and stable.

Now, the various characteristics of the thin film magnetic disk withmicro grooves according to the present invention, together with those ofthe comparison example, will be described in detail.

That is, the magnetic disk according to the present invention has asubstrate having a surface configuration in which the height of the fineprotrusions is between several nm and several tens of nm, whose surfaceroughness Ra is between several nm and several tens of nm, in which thesymmetry Rsk of the sectional curve thereof is negative, preferably,-0.7 or less, and more preferably, -1 or less and which shows athree-dimensional bearing curve in which the sectional area ratio at thesection corresponding to the portion of the fine protrusions which isdeformed by the head load during the CSS drive, i.e., at the sectiontaken at a depth of 5 to 10 nm from portion, is between 0.1% and 10%.The magnetic disk exhibiting such characteristics will be compared belowwith a magnetic disk having a substrate other than that of the magneticdisk according to the present invention.

FIG. 25 shows the results obtained by three-dimensionally measuring thetexture processed surface according to the present invention, and FIG.26 shows the results obtained by measuring the conventional textureprocessed surface in the same manner.

As is clear from the two illustrations, the surface shown in FIG. 25 isvery smooth.

Substrates having different surface configurations were manufactured byconducting texture process under different conditions, including thegrain size of the polishing tape, the times at which the processing headis moved back and forth, the pressurizing force and so on. The differentsurface configurations had fine protrusions of different heights andshowed different surface properties. Thereafter, thin film magneticdisks were manufactured by forming the aforementioned non-magnetic metalfilm, the magnetic medium film, the carbon protective film and thelubricating film on the thus-obtained substrates. FIGS. 13, 14 and 19respectively show the relation between the head floating characteristicsand the head adhesion and the height of the fine protrusions, therelation between the head floating characteristics and the head adhesionand the symmetry, and the relation between the times at which the CSSwas driven and the amount at which the fine protrusions are deformed,i.e., the head-friction. As shown in FIG. 13, when the height of thefine protrusions was several nm (2 to 3 nm) or less, the substrateexhibited excellent head floating characteristics. However, thehead-stickiness increased, and head adhesion, damage to the headsupporting gimbal, overloads to the substrate rotating motor, andcessation of rotation of the substrate occurred. When the height of thefine protrusions was several tens of nm or above, e.g., in a case wherethe fine protrusions were 90 nm or above in height, the head-stickinesswas small, and no head adhesion occurred. However, the head floatingcharacteristics deteriorated, and head crashing occurred. When theheight of the fine protrusions was between 3 and 10 nm, the head floatedstably at a height of 0.15 μm, and the head-stickiness was small.Therefore, the reliable floating characteristic was obtained.

As shown in FIG. 14, the characteristics of the substrate improved whenthe symmetry Rsk was negative, preferably, -0.7 or less, and morepreferably, practically used between -1 and -2.

The relation between the three-dimensional bearing ratio and the headfloating characteristics and the head adhesion (represented by thefriction of the head) is as per description taken in connection withFIG. 32.

The conventional texture processed surface shown in FIG. 26 had asurface roughness Ra of 6 nm, and exhibited a three-dimensional bearingcurve in which the sectional area ratio at the section taken at a depthwhich was 5 nm from the top of the surface was 0.08%. The pressure ofthe head load received by the respective fine protrusions was large. Asshown by the curve D in FIG. 19, as the start-stop-cycles increased,wear of the fine protrusions caused by the sliding of the head advanced,and damage to the lubricating film and carbon protective film proceeded.Furthermore, as the start-stop-cycles increased, the head-frictionincreased, and head crashing occurred. The texture processed surfaceaccording to the present invention, shown in FIG. 25, had a surfaceroughness Ra of 6 nm, and showed a three-dimensional bearing curve inwhich the sectional area ratio at the section taken at a depth which was5 nm from the top portion was between 0.1 and 10%. In this case, asshown by the curve C in FIG. 19, even when the start-stop-cycles wasconducted 30000 times, there was substantially no increase in thehead-friction and no damage to the lubricating film and the carbonprotective film. In the case of the surface which had a roughness Ra of6 nm and which exhibited a three-dimensional bearing curve in which thesectional area ratio at the section taken at a depth which was 5 nm was15%, the area of the disk surface with which it made contact with themagnetic head was large, and the head-stickiness at the initial stage ofthe CSS drive was thus large. Hence, the head supporting gimbal wasdamaged during the rotation of the disk, and cessation of rotation ofthe substrate occurred due to the application of overload to thesubstrate rotating motor.

The above-described embodiment employed the polishing tape to form themicro grooves and fine protrusions on the substrate. However, a surfaceprocessing technique, such as cutting, grinding, lapping or polishing, asurface processing technique such as etching or sand blasting, a drypattern forming technique, or a combination of any of these techniques,may also be performed.

In the above-described embodiment, the polishing tape had a widthsmaller than that of the surface of the substrate which is to beprocessed, and the contact roller for pressing such a polishing tape wasmoved back and forth and at the time vibrated in the radial direction ofthe substrate to process the surface of the substrate. However, apolishing tape having a width close to or larger than that of thesurface to be processed may also be employed. At that time, the contactroller for pressing such a polishing tape may or may not be vibrated toprocess the substrate.

In addition to the Ni--P plated substrate, the above-described textureprocess may also be performed on an Al substrate, a non-magnetic film ora protective film.

As will be understood from the foregoing description, according to thepresent embodiment of the substrate processing method and the apparatussuitable for use in this method, it is possible to provide a magneticdisk which exhibits excellent CSS characteristics even when the heightat which the head floats up is, for example, 0.1 μm. More specifically,it is possible to form a magnetic disk substrate having a surfaceconfiguration in which the height of the fine protrusions is betweenseveral nm and several tens of nm, in which the surface roughness Ra isbetween several nm to several tens of nm, in which the symmetry Rsk ofthe sectional curve thereof is -0.7 or less, and which shows athree-dimensional bearing curve in which the sectional area ratio at thesection corresponding to the portion of the fine protrusions which isdeformed by the head load during the CSS drive, i.e., at the sectiontaken at a depth which is 5 to 10 nm from the top portion, is between0.1% and 10%. In consequence, during the CSS drive in which the magnetichead intermittently makes contact with the surface of the disk, the headload is received by the large number of fine protrusions, and thepressure received by each of the respective fine protrusions is therebyreduced, reducing deformation or wear of the fine protrusions.Furthermore, deterioration in the protective film and the lubricatingfilm formed on the fine protrusions is reduced, and the debris caused bythe sliding of the magnetic head escapes into the deep micro grooves.

Furthermore, in the substrate processing apparatus, since thepressurizing force of the contact rollers against the substrate can bemaintained constant by means of the parallel plate springs, the straingages and the pressurizing force correcting piezoelectric actuatorregardless of the configuration accuracy of the substrate, micro groovescan be formed uniformly and stably over the entire surface of thesubstrate. Furthermore, since the fine protrusions formed on the Ni--Pplated substrate can be removed slightly, the fine protrusions can bemade smooth with a high degree of accuracy.

In addition to the formation of the micro grooves on the surface of thesubstrate, the above-described substrate processing apparatus is alsocapable of removing a very small amount of fine protrusions formed inthe protective film, e.g., a carbon protective film, formed on thesurface of the magnetic disk without damaging the portion of the carbonprotective film or that of the magnetic medium located around the fineprotrusions. In consequence, it is possible to provide a very accurateand smooth surface.

Thus, the present invention provides a highly reliable magnetic disk anda magnetic disk unit which exhibit excellent CSS characteristics evenwhen the height at which the head floats up is low and which allow headcrashing to be eliminated. Provision of the highly reliable disk and thehead and disk assembly can be made possible by providing a magnetic diskmanufacturing method in which the processed surface is estimated usingthe sectional area ratio on the three-dimensional bearing curve thereofand a processing apparatus which includes the first and secondprocessing heads and the washing means used to carry out the first andsecond polishing processes in the above-described manufacturing method.

Next, another embodiment of the present invention will be describedbelow.

Referring first to FIG. 33 which shows a magnetic disk substrateprocessing apparatus employed in the first process of the magnetic diskmanufacturing method according to the present invention, the magneticdisk substrate 2 is held by a retaining tool 98, and is rotated by themotor 3. A plastic working tool 90 is rotatably supported along theradial direction of the disk substrate 2. The plastic working tool 90has micro grooves formed on its circumferential surface, as shown inFIG. 34A and 34B. The plastic working tool 90 is supported by a parallelplate spring 92, on which a strain gage 94 is adhered. The output of thestrain gage 94 is detected by an operation control unit 99 so that apiezoelectric actuator 96 is operated on the basis thereof so as toapply a constant pressurizing force to the parallel plate spring 92.Actually, the plastic working tool 90 is provided at each side of therotating magnetic disk substrate 2, as shown by reference numerals 90₁and 90₂ in FIG. 35. The plastic working tools 90 are pressed against thetwo surfaces of the magnetic disk substrate 2 under a low, constantpressure so that the fine irregularities on the surfaces of the plasticworking tools 90 can be transferred onto the two surfaces of magneticdisk substrate 2 at the same time by means of the plastic deformation.

Next, the second process will be described with reference to FIGS. 36,37 and 12. FIG. 36 shows the process of polishing the two surfacesimultaneously, and FIG. 37 shows the electro polishing process ofselectively polishing the fine protrusions. FIG. 12 shows the knownpolishing process employing the polishing tapes 4.

In the process of simultaneously polishing the two surface shown in FIG.36, only the fine protrusions formed in the surface of the magnetic disksubstrate 2 are polished by placing the magnetic disk substrates 2 heldon a carrier 100 between upper and lower plates 102 on each of which apolishing pad is adhered and then by moving them relative to the plates102 while abrasive grains of, for example, aluminum oxide having anaverage grain size of 0.3 μm are supplied thereto.

In the electro polishing process shown in FIG. 37, the fine protrusionsin the surface of the magnetic disk substrate 2 are selectively polishedby immersing the magnetic disk substrate 2 in a mixture liquid 112contained in an electrolytic bath 110 and then by conducting currentsbetween the magnetic disk substrate 2 and the electrolytic bath 110. Themixture liquid may be a mixture of, for example, sulphuric acid,phosphoric acid and citric acid.

The tape polishing process shown in FIG. 12 employs a polishing tape 4which is composed of a film made of, for example, a polyester, andabrasive grains fixed to the surface of the film. The abrasive grainsmay be aluminum oxide grains having an average grain size of 0.3 μm. Thefine protrusions in the surface of the magnetic disk substrate 2 arepolished by winding the polishing tape 4 pressed against the surface ofthe rotating disk substrate by means of the elastic contact roller 8 andat the same time by moving the tape back and forth in the radialdirection of the substrate.

Now, the results of the experiments in which the magnetic disk substrate2 was processed by the method according to the present invention will bedescribed.

EXAMPLE 1

FIG. 38 shows the results of the experiment obtained by processing theNi--P plated layer 31 formed to a thickness of 10 μm on the aluminumdisk 30 having a surface roughness Ra of 2 to 3 nm, an outer diameter of130 mm and an inner diameter of 40 mm, as shown in FIG. 9, under apressurizing force of 5 N, at a feeding speed of 2 mm/min and at amagnetic disk substrate rotation speed of 50 rpm using the plasticworking tool 90 made of a sintered hard alloy. The surface of theplastic working tool 90 with which the magnetic disk substrate 2 madecontact was spherical and had cuts shown in FIGS. 34A and 34B. Theresults shown in FIG. 38 correspond to those obtained by measuring thesurface of the disk which is subjected to the first process explained inconnection with FIGS. 33 to 35. As is clear from FIG. 38, the surface ofthe magnetic disk substrate 2 has uniform grooves and protrusions ofabout 100 nm formed at a pitch of about 1 μm in its circumferentialdirection. It is also clear that the grooves and protrusions formed onthe surface of the substrate shown in FIG. 38 are farther uniform thanthose formed on the surface subjected to the conventional first process,shown in FIG. 43. Whereas head crashing occurs on the conventionalmagnetic disk whose surface has a cross-section shown in FIG. 43,damaging both the magnetic disk and head, damage to the magnetic diskaccording to the present invention having a sectional force shown inFIG. 38 is far less.

FIG. 39 shows the results of the experiment obtained by conducting thesecond process explained in connection with FIG. 36 on the surface ofthe magnetic disk substrate 2 having the section shown in FIG. 38.Compared with FIG. 38, it is clear that the height of the protrusions onthe surface of the disk 2 are uniform. Abrasive grains employed had anaverage grain diameter of 0.3 μm. A magnetic disk whose surface has across-sectional form shown in FIG. 38 is practical enough. However, anexcellent practical performance is obtained from the second processsubjected to the magnetic disk.

A magnetic disk was formed by forming on the magnetic disk substratewhich has been subjected to the above-described first and secondprocesses the non-magnetic metal film 31 such as Cr to a thickness ofabout 300 μm, the Co--Ni type magnetic medium 32 film to a thickness ofabout 50 μm and the carbon protective film 34 and the lubricating filmrespectively to a thickness of about 50 μm in sequence, as shown in FIG.9. A curve 120 in FIG. 40 shows the results of the CSS test conducted onsuch a magnetic disk. In the CSS test, the magnetic head is brought intocontact with the magnetic disk, and the magnetic disk is rotatedintermittently in that state. As is clear from the curve 120 in FIG. 40,there was no increase in the head-friction of the magnetic diskaccording to the present invention, which was initially 0.04 N, afterthe CSS test was conducted over 10,000 times. Furthermore, the magnetichead floated up above the surface of the magnetic disk stably at aheight of 0.1 μm.

In contrast, the friction characteristic of the conventional diskincreased after the start-stop-cycles exceeded about 100 times, as isshown by a curve 122 in FIG. 40. This increase in the head-frictionincreases occurrence of head crashing.

EXAMPLE 2

FIG. 41 shows the results obtained by measuring the surface roughness ofthe disk which was subjected to the first process and then the secondelectro polishing process shown in FIG. 37. A mixture liquid containing54 wt % of sulphuric acid, 45 wt % of phosphoric acid and 1 wt % ofcitric acid was used as the electrolyte. Currents having a density of4.5 A/cm² was conducted to the electrolyte having a temperature of 30°C. for 1 minute. As is clear from FIG. 41, the protrusions wereselectively polished and were made uniform. A magnetic disk wasmanufactured by conducting the surface process shown in FIG. 9 on thethus-obtained substrate. When the CSS test was conducted on the obtainedmagnetic disk, the same result as that shown by the characteristic curve120 in FIG. 38 was obtained.

EXAMPLE 3

The tape polishing process shown in FIG. 12 was conducted as the secondprocess on the disk on which the first process was conducted. Thesurface roughness of the obtained disk was almost the same as that shownin FIG. 39. Therefore, the same result as that shown by the curve 120 inFIG. 40 was obtained when the CSS test was conducted on the disk. Apolishing tape, which was a polyester film to which aluminum oxidepowders having a grain size of 0.5 μm were fixed, was employed.

EXAMPLE 4

The second process was conducted on the surface of the disk 2 which wassubjected to the first process by winding the polishing tapes 4 pressedagainst the surfaces of the disk 2 by means of the air stream blown fromnozzles 130 as shown in FIG. 42 and at the same time by moving the tapes4 back and forth in the radial direction of the disk 2 as the tapes 4are wound. The surface roughness of the obtained disk was similar tothat shown in FIG. 39. Therefore, the same result as that shown by curve120 in FIG. 40 was obtained when the CSS test was conducted. A polishingtape, which was a polyester film to which aluminum oxide powders havinga grain size of 0.5 μm were fixed, was employed.

The method of processing the single magnetic disk has been described. Itis also possible to mass produce duplicates of the magnetic diskobtained by the above-described processing method according to thepresent invention.

A mold 140 of the recording surface of the magnetic disk 2 which issubjected to the first process or both the first and second processes,as shown in FIG. 44, may be formed by coating nickel or the like on therecording surface by means of the electroplating, and the form of therecording surface on the mold or on a harder mold manufactured from thethus-obtained mold may be transferred onto plastic magnetic diskpatterns so as to manufacture magnetic disks Alternatively, the form ofthe recording surface of the mold 140 may be transferred onto thesurface of the aluminum magnetic disk patterns coated with a plastic bymeans of the thermal plastic working or the like so as to manufacturemagnetic disks.

The duplicating method shown in FIG. 43 is very difficult to apply tothe conventional magnetic disk having a cross-sectional form shown inFIG. 43 for the following reasons: Firstly, the sectional form shown inFIG. 43 has so deep cuts or overhangs (the protrusions which overhangthe pits) that they may be partially removed when the duplicates areseparated from the mold. Secondary, a high accuracy is required for themold employed for the mass production, and it is impossible to judge theaccuracy of the mold onto the sectional form shown in FIG. 43. Theabove-described duplicating method can therefore be applied only to thecase in which the plastic magnetic disk patterns are manufactured usinga tool with which the surface configuration can be formed with a highdegree of accuracy, as in the case of the present invention.

Furthermore, it is not always necessary for the duplicating method toemploy the plastic working tool such as that shown in FIG. 34A, 34B.Normal precision machine tools or machines used for manufacturingdiffraction gratings may also be employed. This is because the presentinvention is directed to provision of the recording surface of amagnetic disk on which uniform and accurate irregularities are formed,as shown in FIGS. 38 and 39.

As will be understood from the foregoing description, in the presentinvention, the rough irregularities formed on the surface of the diskduring the first process in the conventional processing method can bechanged into the fine and uniform irregularities. Furthermore, lappingof the protrusions can be conducted in the second process effectively.In consequence, even when the times at which the contact start-stopstest was conducted on the magnetic head and the magnetic disk exceeded10,000, the surface pressure of the magnetic head was low, and themagnetic head floated up stably. It is thus possible to greatly prolongthe life of and improve the reliability of a magnetic disk unit.

Furthermore, since the pitch or the depth of the irregularities on thesurface of the magnetic disk can be freely set by using an arbitraryprocessing tool, the present invention can be applied to magnetic diskshaving various form and applications.

Furthermore, even when the height at which the magnetic head floats upis 0.1 μm, the magnetic head does not make contact with the disk, andthe stable floating characteristics are assured. In consequence, therecording and reproduction sensitivity of a magnetic disk unit can beimproved, and the recording density of the magnetic disk can thereby beincreased.

Another embodiment of the present invention will be described below.

FIGS. 34A and 45B show different processing tools that can be employedin the processing apparatus shown in FIG. 33. The processing tool shownin FIGS. 34A and 34B will also be described below.

The cylindrical processing tool 90 is rotatably supported on a shaftwhose axis is directed in the radial direction of the disk which is tobe processed. The processing tool 90 is pressed against each of the twosurfaces of the disk 2. The cylindrical surface of the processing tool90 shown by the reference numerals 90₁, 90₂, 90₃ and 90₄ in FIGS. 34A,45A and 46A has fine regular grooves and protrusions. The surface of theprocessing tool 90 is coated with diamond.

The operation control unit 99 shown in FIG. 33 compares the output ofthe calculation with a preset pressurizing force, and operates thepiezoelectric actuator 96 and thereby drives the parallel plate spring92 in the axial direction of the disk 2 such that the pressurizing forceof the processing tool 90 can be maintained constant.

When the disk 2 is to be processed by means of the thus-arrangedprocessing apparatus, the processing tool 90 is pressed against therotating disk 2 under the set under while it is moved back and forth inthe radial direction of the disk 2, by means of which the fine regulargrooves and protrusions on the surface of the processing tool 90 aretransferred onto the surface of the disk 2.

Next, the examples of processing the surface of the disk using theapparatus shown in FIGS. 33 and 35 and the processing tool 90 havingvarious forms will be described.

EXAMPLE 1

A Ni--P plated aluminum disk, which had an outer diameter of 130 mm, aninner diameter of 40 mm, and a thickness of 2 mm, and which was polishedto a surface roughness Ra of 2 to 3 nm, was processed under apressurizing force of 5 N, at a disk rotational speed of 50 rpm and at aprocessing tool feed speed of 2 mm/min using the processing tools 90₁and 90₂ each of which was a sintered hard alloy and with diamond coatedthereon. The sintered hard alloy had an outer diameter of 30 mm and awidth of 10 mm, and the surface thereof with which the disk makescontact was spherical. The surface of the sintered hard alloy had cutsshown in FIGS. 34A and 34B. FIGS. 49A and 49B show the results obtainedby measuring the processed surface. Micro grooves and protrusions weretransferred in the circumferential direction of the disk, and thesection taken in the radial direction of the disk (in the directionindicated by the arrow in FIG. 49A) had a form shown in FIG. 49B inwhich the maximum height was between 40 and 50 nm and in which thegrooves and protrusions were formed at a pitch of about 1 μm.

EXAMPLE 2

The aluminum disk was processed under the same conditions as those ofExample 1 using the processing tool 90₃ which was the same sintered hardalloy as that employed in Example 1 with the diamond coated thereon. Thesurface of the sintered hard alloy had regular cuts which extended inthe direction perpendicular to the direction in which the processingtool was rotated, as shown in FIGS. 45A and 45B. FIGS. 50A and 50B showthe results obtained by measuring the processed surface. Micro groovesand protrusions were transferred radially in the radial direction of thedisk, and the section taken in the circumferential direction of the disk(in the direction indicated by the arrow in FIG. 50A) had a form shownin FIG. 50B in which the maximum height of the protrusions was between40 and 50 nm and in which the grooves and protrusions were formed at apitch of about 1 μm.

EXAMPLE 3

The aluminum disk was processed under the same conditions as those ofExample 1 using the processing tool 90₄ which was the same sintered hardalloy as that employed in Example 1 with the diamond coated thereon. Thesurface of the sintered hard alloy had regular grooves and protrusionswhich extended in a direction perpendicular to the direction in whichthe processing tool was rotated, as shown in FIGS. 46A and 46B. Thepitch of the protrusions was large. The bottom of the grooves was flat.FIGS. 51A and 51B show the results obtained by measuring the processedsurface. Micro grooves and protrusions were transferred radially in theradial direction of the disk, and the section taken in thecircumferential direction of the disk (in the direction indicated by thearrow in FIG. 51A) had a form shown in FIG. 51B in which the surfacelayer of the disk was flat and in which the grooves were formed at apitch of about 2 μm.

COMPARISON EXAMPLE

FIGS. 55A and 55B show the results obtained by measuring the surface ofthe disk which was subjected to the conventional polishing process(disclosed in Japanese Patent Unexamined No. 54-23294). The sectiontaken along the radial direction of the disk (in the direction indicatedby the arrow in FIG. 55A) had a form shown in FIG. 55B. Grooves andprotrusions having a maximum height of about 50 nm were formed at anirregular pitch.

The present inventors examined the floating characteristics of the disksprocessed by the disk manufacturing method according to the presentinvention and those of the disks processed by the conventional diskmanufacturing method, and found that the surface of the disk processedby the disk manufacturing method according to the present inventionshowed small variations in the form and had reduced fine protrusions,and that the disk processed by the disk manufacturing method accordingto the present invention thus exhibited greatly improved head floatingcharacteristics. In particular, in the case of the disk obtained inExample 2, stable air stream was generated between the magnetic head andthe disk during the rotation of the disk, and the magnetic head easilyfloated up due to the dynamic pressure effects. Furthermore, vibrationsof the floating magnetic head were reduced, and the output noises werethus greatly reduced.

On the other hand, the surface of the disk processed by the conventionaldisk manufacturing method had irregular grooves and protrusions. Thepresence of the fine protrusions of burrs deteriorated the head floatingcharacteristics and the CSS characteristics.

Also, the present inventors measured the Abbott-Firestone curve in theradial direction of the disks processed by the disk manufacturing methodaccording to the present invention and of those processed by theconventional disk manufacturing method, and found that the bearing ratioat the section taken at a depth of 5 nm of the disk processed by theconventional disk manufacturing method was about 10%, as shown in FIG.54. The surface configuration of that disk varied a lot when the CSSdrive was repeatedly conducted. The present inventors also found thatthe bearing ratio at the section taken at a depth of 5 nm of the disk ofExample 3 was 50% or above, as shown in FIG. 53. Since the area of thedisk with which the head was brought into contact was large, the surfaceconfiguration did not vary when the CSS drive was repeatedly conducted.The durability of the disk surface thereby greatly improved.

FIGS. 47 and 48 respectively show the different relations between thethin film magnetic disks 2A and 2B having different structures accordingto the present invention and the magnetic head 81.

The surface of the disk 2A shown in FIG. 47 has grooves which extendradially in a direction perpendicular to the direction of rotation ofthe disk 2A, i.e., in the radial direction thereof, and which have asaw-tooth form which is asymmetrical with respect to the direction inwhich the disk 2A is rotated. In consequence, a stable air flow isgenerated between the magnetic head 81 and the disk 2A while the head isfloating in the air, generating dynamic pressure effects whichaccelerate floating of the magnetic head 81 at a constant height.Furthermore, vibrations of the floating head are reduced, and the outputnoises are thereby reduced.

The surface of the disk 2B shown in FIG. 48 has a large area with whichthe head makes contact, i.e., has a large bearing ratio. In consequence,changes in the form of the disk 2B caused by the contact of the magnetichead 81 are less. Furthermore, since the lubricant can be retained inthe grooves provided at equal intervals, it remains on the surface ofthe disk 2B even after the CSS was repeatedly conducted, and increase inthe CSS friction can thereby be restricted.

In the case of the disks 2A and 2B, since no burrs are generated, nofine protrusions are present. In consequence, even when the headfloating height is low, the head does not make contact with the disk 2Aor 2B, and no head crashing hence occurs.

The above-described examples employed the cylindrical processing toolcoated with diamond. However, very hard and fine grains such as TiCgrains may also be used. A processing tool whose surface with which thedisk makes contact is conical or spherical may be employed in place ofthe cylindrical processing tool. Alternatively, a processing tool whosesurface with which the disk makes contact has micro grooves andprotrusions or is coated with very hard fine grains such as diamond orTiC grains may also be used. Furthermore, the above-described examplesemployed the aluminum disk. However, plastic working may be conducted ona non-magnetic intermediate film or a magnetic medium film coated on thesurface of the substrate by the sputtering or the plating.

In the disk processing apparatus according to the present inventionshown in FIGS. 33 and 35, the fine pressurizing force is maintainedconstant by employing the parallel plate spring on which the strain gageis adhered. However, the plastic working tools 90 may also be pressedagainst the surfaces of the disk 2 by rotatably supporting the plasticworking tools 90 on a pair of rods 150 in such a manner as to be movablein the axial direction of the disk 2, as shown in FIG. 52, and byattracting the rods 150 to each other by means of a tension spring 160.The tension spring 160 may be replaced by an air cylinder whose slidingresistance is reduced as much as possible or a method of employing amagnetic force.

As will be seen from the above description, in the present invention,texture can be uniformly formed on the surface of the magnetic disk,enabling a clean and highly reliable magnetic disk surface to be formed.Furthermore, the tool has a relatively long life, and is therebyeconomical. The tool can easily be cleaned. Particularly, scratches orremains of the processing can be eliminated, and yield can thereby beimproved.

Furthermore, since the maximum height or pitch of the texture formed onthe surface of the disk can be freely set, the head floatingcharacteristics can be improved. Furthermore, since the texture has anuniform form with no fine protrusions and a large area with which thehead makes contact and, hence, a large bearing ratio, the durability ofdisk surface can be greatly improved. Furthermore, since the texture canbe formed radially in the radial direction of the disk, which isimpossible conventionally, and the dynamic pressure effects can begenerated between the head and the surface of the disk, the headfloating characteristics can be greatly improved.

What is claimed is:
 1. A magnetic disk comprising a non-magneticsubstrate with a surface processed layer having fine irregularitiesformed at least on a main surface thereof, said surface processed layerof said non-magnetic substrate having protrusions whose surfaces areessentially made level, and having a surface configuration, whichexhibits a three-dimensional bearing curve, and has a bearing ratio ofbetween 0.1% and 10% at a depth from a top of the protrusions whichcorresponds to a portion of the surface processed layer deformed by ahead load during contact start-stop operation, and a thin film magneticlayer and a protecting layer are formed in that order on saidnon-magnetic substrate in such a manner that said fine irregularitiesare duplicated thereon.
 2. A magnetic disk according to claim 1, whereinsaid non-magnetic surface processed layer has a surface configurationwhich exhibits a three-dimensional bearing curve in which a portion ofthe curve which represents a surface layer thereof is flat.
 3. Amagnetic disk according to claim 1, wherein said surface processed layerof said non-magnetic metal substrate has a surface characteristic inwhich a micro groove having a depth of at least 100 nm is present withina length thereof corresponding to the width of a head slider slidingsurface and in which a symmetry of a sectional curve thereof is equal toor smaller than a negative value -0.7, wherein the negative valuerepresents that the sectional curve has a larger depth component than aprotrusions component.
 4. A magnetic disk according to claim 1, whereinsaid irregularities on said surface processed layer comprise regulargrooves and protrusions formed on a recording surface of said magneticdisk in a circumferential direction thereof.
 5. A magnetic diskaccording to claim 4, wherein said regular grooves and protrusions areformed by a plastic working technique.
 6. A magnetic disk according toclaim 4, wherein said regular protrusions have a polished top portion.7. A magnetic disk set forth in claim 4, wherein said substrate is usedso as to make a recording surface transferred by using a duplicate ofsaid substrate.
 8. A magnetic disk according to claim 4, wherein saidgrooves and said protrusions are formed by means of a cylindrical,drum-like, spherical or conical plastic working tool which is rotatableabout a central axis thereof and which has a surface on which microgrooves are formed in a circumferential direction thereof.
 9. A magneticdisk according to claim 1, wherein a non-magnetic intermediate film anda magnetic medium film are coated on the surface of said substrate, andwherein micro grooves and protrusions are formed on said magnetic mediumfilm.
 10. A magnetic disk comprising a non-magnetic substrate with asurface processed layer having fine irregularities formed at least on amain surface thereof, said surface processed layer of said non-magneticmetal substrate having protrusions whose height ranges from severalnanometers to several tens of nanometers and whose surfacecharacteristics are essentially made level, and having a surfaceconfiguration which exhibits a three-dimensional bearing curve, and hasa bearing ratio of between 0.1% and 10% at a section taken at a depth of5 to 10 nm from a top of the protrusions, and at least a thin filmmagnetic layer and a protecting layer are formed in that order on saidnon-magnetic substrate in such a manner that said fine irregularitiesare duplicated thereon.
 11. A magnetic disk according to claim 10,wherein said non-magnetic surface processed layer has a surfaceconfiguration which exhibits a three-dimensional bearing curve in whicha portion of the curve which represents a surface layer thereof is flat.12. A magnetic disk according to claim 10, wherein said surfaceprocessed layer of said non-magnetic metal substrate has a surfacecharacter in which a micro groove having a depth of at least 100 nm ispresent within a length thereof corresponding to the width of a headslider sliding surface and in which the symmetry of a sectional curvethereof Rsk is equal to or smaller than a negative value -0.7, whereinthe negative value represents that the sectional curve has a largerdepth component than a protrusion component.
 13. A magnetic diskaccording to claim 10, wherein said irregularities on said surfaceprocessed layer comprise regular grooves and protrusions formed on arecording surface of said magnetic disk in a circumferential directionthereof.
 14. A magnetic disk according to claim 10, wherein anon-magnetic intermediate film and a magnetic medium film are coated onthe surface of said substrate, and wherein micro grooves and protrusionsare formed on said magnetic medium film.